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New generic Venus Filter

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#1 NA_joey

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Posted 29 November 2018 - 15:16

New UV Venus Fliter on the market on eBay.
I just won and auction for one. For $52gpb and shipping 8gpb.

https://www.ebay.com...a-/382649866784

learance - £1.00 start and NO RESERVE!!

One of our High Transmission (HT) precision range of filters, this 2" Venus U filter is sure to impress on performance, quality and price. It comes with its own individual data sheet of performance - guaranteed!

Our filter benefits from the amazing technology that enables a precise bandwidth between 280-380nm with exceptional cut off each side and a peak transmittance of >80%. Only for use imaging with large telescopes (our eyes cannot see in this bandwidth). This filter will allow you to photograph in the deep UV - an area normally off limits.

Specification

Astronomical Filter Venus U
Dia Tolerance 0/-0.1mm
Thickness Tolerance ±0.1mm
Substrate Schott RG610
Incident Angle 0°
Optical Data
FWHM=70nm±5nm

Tp>80% 350nm±3nm

Tave<0.5@>380nm

Quality Surface 60/40



Performance

Our filters offer performance as good as, and in some cases better than, the top brands currently on sale. The listing shows a typical performance curve for the Venus U filter (if you are unsure how to interpret the graph see our easy to read Glossary guide below). You can compare this to similar curves from the top brands and we are sure you will be pleasantly impressed.

However, to ensure that you will be impressed with your purchase each filter is individually tested and issued with its own performance data sheet. This is your guarantee that you are getting exactly what you paid for. Of course, there will be minor variations but the specification quoted is the minimum that you will get.

Quality
Each filter is built upon a precision polished substrate of Schott glass. The specification speaks for itself and is supported by the data sheet. The filter will retain its 'as new' optical performance for more than 10 years. It is resilient to scratches, moisture, dew, and humidity.

Even the storage package was carefully developed to take the greatest of care of your filter so that it can be a long lasting companion to you and your hobby or profession.

Price
No silly RRPs but an honest price for an outstanding product.

Sky's the Limit are pioneers in bringing exceptional value items to the astronomy market. Started in 2004 we have been importing and selling optical products at prices others only wish they could achieve. By dealing directly with the manufacturers and suppliers in China and keeping our overheads low in the UK we are at the forefront of the bargain price supply chain. We aim to be the lowest prices in the UK and we aim to offer the best service that you would get from anywhere. Our integrated warehouse and distribution facility is linked directly to Paypal so that your order can be processed and dispatched without delay.

Short Glossary of terms relating to filters

Term Definition
Clear Aperture The surface area of an optical filter which is free of any defects or obstructions. On interference filters the clear aperture is often delimited by an annulus of metal or opaque material.
CWL Centre Wave Length. For optical bandpass filters, the arithmetic mean of the cut-on and cut-off wavelengths at 50% of peak transmission.
Dia Tolerance (diameter tolerance) Accuracy of construction of the diameter of the filter
FWHM (Also called Bandwidth) FWHM (Full width at half of maximum transmission). For optical bandpass filters, typically the separation between the cut-on and cut-off wavelengths at 50% of peak transmission. Sometimes a bandwidth at, for example, 10% of peak transmission is specified or it is specified in nm.
Incident angle The angle formed by a ray incident on a surface and a perpendicular to the surface at the point of incidence.
Quality Surface
Scratch/Dig

A set of specifications for defining the maximum allowable size and number of scratches and digs on an optical surface. The scratch/dig values (e.g., 60/40) specify the scratch width in microns and the dig diameter in tens of microns, respectively. Although extensive evaluation procedures exist if rigorous standards must be maintained (military specification MIL-F-48616, for example), a qualitative visual assessment of the scratches and digs usually suffices.

Substrate The ground and polished piece of optical glass that is used as a base for the filter coating. Schott B270, HB610 or RG610
T ave

Transmission Average

The average calculated over the useful transmission region of a filter rather than over the entire spectrum. For a bandpass filter, this region spans the FWHM of the transmission band.

Thickness Tolerance Accuracy of construction of the thickness of the filter
Tp
Peak Transmission

The maximum transmission attained by a bandpass filter, expressed in percent. Required peak transmission of a bandpass filter may be specified as minimum peak transmission to be 70 percent. Note that peak transmission usually occurs at the centre wavelength.




#2 Andy Perrin

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Posted 29 November 2018 - 16:13

This spec sheet does not make any sense! The sheet says the substrate is RG610.

Quote

Specification

Astronomical Filter Venus U
Dia Tolerance 0/-0.1mm
Thickness Tolerance ±0.1mm
Substrate Schott RG610
Incident Angle 0°
Optical Data
FWHM=70nm±5nm

Tp>80% 350nm±3nm

Tave<0.5@>380nm


Quality Surface 60/40

Spectrum of RG610:
Attached Image: Screen Shot 2018-11-29 at 11.19.35 AM.png

Can anyone tell me how you can make a UV filter out of a substrate that blocks UV?

Quote

Quality
Each filter is built upon a precision polished substrate of Schott glass. The specification speaks for itself and is supported by the data sheet.
Heh.

Edited by Andy Perrin, 29 November 2018 - 16:21.


#3 JMC

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Posted 29 November 2018 - 16:33

Glad it wasn't just me that thought the specs didn't make any sense at all. Might keep an eye on them and try and pick one up, but I won't be spending 50 quid on one to try it out.

#4 OlDoinyo

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Posted 29 November 2018 - 19:36

Perhaps that is a typo in the spec sheet?! I would be interested to hear results if the buyer has a chance to test this!

#5 NA_joey

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Posted 29 November 2018 - 20:38

Ill let you know I have a real Venus filter to compare too

#6 NA_joey

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Posted 29 November 2018 - 20:48

I am a risk taker I guess it’s eBay monkey back grants no lost ever.

#7 Cadmium

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Posted 29 November 2018 - 23:23

Looks interesting. Certainly the 610 is wrong.
Take a look at the graph, seems to start leaking around 900/1000nm?
Not sure what the actual out of band OD would be...? If the 610 is wrong, then what else is wrong?
Proof is in the pudding, as they say.
Take a pic with it, stack it with some longpass filter, take another pic using the same settings and exposure time, and see if there is any faint image, AKA IR leak.

#8 Reed F. Curry

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Posted 30 November 2018 - 00:08

The >380nm transmission is <0.5 avg. To get any decent blocking, I think you would need a UG11 and an NIR blocking glass. In that case, the dichroic filter is not needed at all. :)

Edited by Reed F. Curry, 30 November 2018 - 00:14.

Best regards,
Reed
http://www.uvroptics.com

#9 Andy Perrin

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Posted 30 November 2018 - 05:07

Quote

The >380nm transmission is <0.5 avg.
Which is another issue with that sheet. How exactly do they get a <0.5 average transmission when the graph they show looks like this:
Attached Image: Screen Shot 2018-11-30 at 12.06.56 AM.png
Do they average down to 200nm?

Edited by Andy Perrin, 30 November 2018 - 05:09.


#10 Andrea B.

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Posted 30 November 2018 - 15:35

This is all very interesting. The Sky's the Limit (Ebay) company seems to have a good Ebay rep with thousands of transactions. Somewhere I read that filters were made by Optolong (in China), but now I cannot find that to make a link for you.

On Optolong's website the VenusU shows a rather large bump between 850-900 nm. That does not appear on the above chart. The substrate is listed by Optolong merely as "Schott" with no reference to RG610. That's probably an error.


The address for Sky's the Limit in England is someone's house. So it is a mail order only business.

If you go to the non-Ebay website, prices are cheaper.
Andrea G. Blum
Often found hanging out with flowers & bees.

#11 Andrea B.

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Posted 30 November 2018 - 16:03

The real question is whether Optolong is importing Schott glass at lower prices than what every other place is paying for it?
Andrea G. Blum
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#12 dabateman

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Posted 30 November 2018 - 19:41

Andrea,
That makes sense. When I looked at the picture it reminded me of the Astrodon Venus filters. However, they are more bluish in their generic filter pictures.

My feeling is that there are a bunch of none perfect seconds off the line. These are most likely sold cheap, to recoup the costs, just like some other scientific filters sold on ebay. This I think is also why the description indicates that the sheet is an example of a filter. My guess is that its the best case.

I also now see that this ebay listing has been pulled down as the filter is no longer available. Did you buy it Andrea directly from the sellers site? They say they will pull down listings if purchased directly from them.

#13 Cadmium

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Posted 30 November 2018 - 23:21

View PostAndrea B., on 30 November 2018 - 16:03, said:

The real question is whether Optolong is importing Schott glass at lower prices than what every other place is paying for it?

Seems to me the 'real question' is if the filter works for UV only photography with no visual or IR leaking.
Given all the info, it would seem not, but it would be easy to test.
They are probably importing the dichroic filter from China, with their custom name printed on it by the Chinese, and it is probably not even a Schott glass substrate.
Naw, you can't import Schott glass cheaper, you either get it from Schott or get it from a reseller.

#14 Andrea B.

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Posted 01 December 2018 - 00:37

I won't buy Chinese made filters at this time because I want the real deal, something I can trust. If manufacturing standards improve, then perhaps I will later.
Andrea G. Blum
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#15 dabateman

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Posted 01 December 2018 - 06:36

Based on the cost, location and confusing details, I don't think they would be using Schott glass. Most likely its a coated sheet of Zwb1 glass.

Transmission data is a relative measurement. The reference is not provided in that data sheet. It could be air, and 80% would be great. It could be an uncoated sheet of Zwb1, and 80% would be less ideal. Or it could even be a coke bottle found in the cafe, then 80% is disappointing.

Just looked up the new Astrodon sloan Gen 2 U filter and prices have really shot up on that one. Now $500 for the 50mm round filter direct from them. I guess after being bought out they need to make money.
After I broke my BaaderU, not that long ago I was considering this filter, but it was about $300.

Edited by dabateman, 01 December 2018 - 07:32.


#16 Cadmium

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Posted 01 December 2018 - 09:10

I don't think these dichroic UV astronomy filters are unusual at all, go to any astronomy site, and you will see similar filters, but the best would be the Baader U.
The unusual part would be a less expensive price for such a filter that performs up to our standards with no visual or IR leaks, no warm or gray black Rudbeckia centers... etc..
Most of us know what that means here.
All it takes is for someone to test the filters and find out.
Don't get your hopes up too high, because most of the astronomy filters like that don't perform up to our standards, other than the Baader U.
Given the data and graph I see presented with the "Sky's the Limit 2" Venus U Premium" I would wait for a test before assuming anything.
Still, it is interesting.
Who cares where the glass is from, it is the substrate, it is a dichroic filter, the performance is what matters.
Where the glass is from is only an assumption or guess anyway, we already know it is not made out of what it says, RG610...?... Hey, it isn't 'rocket science' to know that doesn't fly.

#17 WiSi-Testpilot

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Posted 01 December 2018 - 09:32

Would the Astrodon sloan Gen 2 U filter perform up to the standards here? It costs $400 at the moment. The advantage of an unmounted filter would be that I save the weight for 2 adapter rings compared to Baader U (which is still not available at Baader). I will ask my optometrist next week whether they are able to mount it in a 49 mm mount of a filter, for instance. Some time ago they processed a BG3 filter, but it has no coating.
Best regards,
Wilhelm

Attached Images

  • Attached Image: Brille-Kameragehäuse.jpg


#18 Cadmium

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Posted 01 December 2018 - 10:55

BG3 needs no coatings.
I would get the Baader U instead of the Astrodon.
You can remount a Baader U like this if you want, whatever size you want it to be.
Attached Image: baader_U_step_down.jpg

#19 WiSi-Testpilot

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Posted 01 December 2018 - 11:22

Thank you, that looks very good!
Best regards,
Wilhelm

#20 UlfW

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Posted 01 December 2018 - 12:28

View PostCadmium, on 01 December 2018 - 10:55, said:

I would get the Baader U instead of the Astrodon.
You can remount a Baader U like this if you want, whatever size you want it to be.

I would prefer the Baader U too if weight is very important.
When remounting my 2" Baader U i used a step up ring, 48 to 52mm, instead of the retaining ring shown in the picture above, to get a front thread for a lens shade.

I have decided to use 52mm filters as my main thread standard for filters in the UV-range as most of my UV-capable lenses work well with that.

Edited by UlfW, 01 December 2018 - 12:47.

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