Hello from Singapore

[BruceG]

Hi all,

 

Bruce from Singapore here, I'm a film student and have strong passion in photography. I have my J5 mirrorless converted to full spectrum and did some IR, then I decided to explore UV and and found out about UVP and have since spent time reading the posts and learning. UV is so much harder than IR but can be more rewarding at the same time. I think there is great potential for both technique to be used for creative effect in filmmaking, I'm especially intrigued by how UV portrays human subject and landscape.

 

I'm really glad to become a member and hope to contribute to the discussions soon as I get better.

 

Some questions I have:

Black clothes sometimes looks purple under full spectrum, is it due to UV? Is there a quick way to test a camera's UV pick up?

Has anyone had experience with Sigma/Ricoh C mount 25 f2.8 UV lens? It's field fits Nikon 1 sensor just nice and I'm thinking of getting one.

Thank you!

[nfoto]

Welcome to us on UVP ... I'm certain this will be of dual benefit to all parties.

 

As to your lens, industrial optics tend to be designed for a narrow wavelength range and if used outside that range, lots of chromatic aberrations and other optical artefacts can occur. I looked through the specification on the Ricoh site and it apparently is a candidate for UV work if you fit a proper UV bandpass filter over it. Do remember the need for efficient IR blocking if you wish to do pure UV. The small filter size might necessitate using step rings, though, always a hassle and something prone to get stuck in the threads if you use more than one size to arrive at the final filter threads.

 

Anyway, do keep us informed on any progress and don't hesitate to ask questions.

[BruceG]

Thank you Bjørn, in fact I have just ordered the lens from a local distributer of pentax cctv lens, it is cheaper than the price listed on B&H, waiting for it to arrive now. I looked for Baader U at the local astronomy shop but they don't even have, so I ordered some filters including ZW1 from online. Yup the IR leak would be problem I need to slove, will report my finding when I have my hand on the lens.

[Andrea B.]

Hello Bruce and welcome to UltravioletPhotography.com. We are looking forward to your experiments with the J5 and the lens you mentioned.

 

As for UV-pass filters, there are others besides the BaaderU.

We have information in the Filters Sticky: Sticky :: UV/Vis/IR Filters

Info about IR-blocking is also there.

 

You can also search for filter tests using the Filter Tag: Filters

 

I haven't tested that ZW1 yet but should probably try to do so. :)

[BruceG]

Thank you, Andrea!

[BruceG]

I happened to find these filters under short pass filter in Edmund optics:

http://www.edmundoptics.com.sg/optics/optical-filters/shortpass-edge-filters/shortpass-filters/47285/

http://www.edmundoptics.com.sg/optics/optical-filters/shortpass-edge-filters/dichroic-shortpass-filters/69200/

Can anyone tell me can they be useful for UV photography?

[nfoto]

They have transmission in the visible that although small still might be troublesome if 'pure' UV photography is your main aim..

 

I think it is better to play safe and use the filters more commonly discussed here on UVP. Whilst many of these tend to be provided in fairly large size, 52 mm being an unofficial common standard, most can be had smaller. Baader sells their 'Venus' in 1.25" and that should be close to what your lens requires. I'm sure other contributors here chip in with alternate suggestions as well.

[Andrea B.]

I do not have any specific information about the two referenced Edmund filters.

 

However, one thing to be aware of is that some hard-coatings on filters can be almost mirror-like. This makes such filters very difficult to use for our typical uv photography because it creates a lot of reflective flare which washes out the photo.

See here for one such example: link.

[nfoto]

An overlooked qurestion from an earlier post

 

"Black clothes sometimes looks purple under full spectrum, is it due to UV?"

 

Probably IR.

[Andrea B.]

Indeed.

 

The purple-black phenomenon from IR contamination is particularly evident in synthetic fabrics when photographed with an unfiltered camera.

 

Remember when the first digital Leica M8 came out and everyone was upset with the colours because blacks were looking washed out? Turns out the M8 had no internal IR blocking filter. So Leica had to make some external "hot mirrors" available to everyone. I think I got one free one. Paid for another. (Didn't keep the M8. Not my style.)

[BruceG]

I see, what I thought was IR would be interpreted as red, it seems then the blue color filter under the microlens do pass through IR too.

Regarding the Short pass filters from Edmund optics, I studied their curves and my conclusion is that they are not worth the investment because they are not effectively blocking other wavelength. However, one particular item caught my attention and I think it is possible to be used for IR blocking, in place of filters like S8612. The curve provided does not cover full spectrum, but from the specs it is said to have used Borofloat which has good UV transmission. I think it is worth a try:

http://www.edmundoptics.com.sg/optics/optical-filters/color-dichroic-filters/additive-subtractive-dichroic-color-filters/52537/

Also, I just realised the sensor is still covered by a layer of glass after removing the internal filters, it seems to be fused with the sensor, has anyone tried to removing it?

[colinbm]

Interesting filter Bruce, but it needs to be known how well it blocks the red / IR leak in UV filters, but it is affordable.

Some astro-photographers remove the sensor cover glass & scrape off the micro-lenses & colour dyes, but there appears to be no advantage in UV photography.

Col

[BruceG]

Thanks Col, I will leave the cover glass then in this case.

I also just found out there is a IR emittig source inside my J5, a 30s exposure reveals the problem. I am stuffing the space inside the camera with toilet paper I dyed black, the dye is graphite based and does not reflect IR, hope it works.