Graduating to a higher class of forum

[ulf]

The UV-Nikkor is a great enabler, because you can frame and focus in visible light so that the dSLR viewfinder is completely usable and LiveView is not required. The original 1985-1999 series was especially nice, as it came with a flip-down filter holder which allowed the user to focus in visible, then simply flip the filter up and shoot in UV. Mine is from the 2006+ series and doesn't have the convenient filter holder, so I have to keep screwing the filter off and on. Fortunately, adding a rubber hood has made that operation much more secure and quick to perform.

Changing the amount of (filter) glass in the light path in front of the lens will change the focal distance slightly. That might be significant in higher magnifications if the focus shift of the lens is not dominant.

I do a lot of filter swapping with different filter stacks and the magnetic filter holder system Xume from Manfrotto works very well for me. https://www.manfrotto.co.uk/xume

[nfoto]

Swapping filters is easier when one mounts a K3 ring on the lens and puts the filters into K2 rings. Then there is a simple bayonet connection that allows swapping without screwing on-off.

 

This works perfectly with the 52mm thread of the UV-Nikkor.

[Andrea B.]

The UV-Nikkor is a great enabler, because you can frame and focus in visible light so that the dSLR viewfinder is completely usable and LiveView is not required.

 

Weeeellllll.......Focusing the UV-Nikkor in visible light gets you close enough for most work. But I've been shooting that UV-Nikkor since '07 and have found that focusing it in Live View through the UV-pass filter is the best practice. Even my Ultra-Achromat-Takumar 85/4.5 is not perfect when focused first in visible light. Nor the CO 60/4.0. (Somewhere on UVP a couple or 3 years ago there are some examples showing missed focus from the UAT.) Not sure I can tell you why this is so, but seems to have something to do with thickness of filter and distance from subject. Like for close work (which is most of what I do), focus is often missed when using the visible method.

Oh well. Just thought I'd toss in my experience on this. Everyone's MMV.

 

BTW, you can still sometimes find those flip filter holders on Ebay. Often the flip's foam lining has deteriorated, but it's not too much trouble to scrape out the old foam and add a new thin layer of padding.

Example picked at random: Nikon AF-1 Gelatin Filter Holder

Step rings will also be needed if using Baader-U.

[dabateman]

 

Changing the amount of (filter) glass in the light path in front of the lens will change the focal distance slightly. That might be significant in higher magnifications if the focus shift of the lens is not dominant.

I do a lot of filter swapping with different filter stacks and the magnetic filter holder system Xume from Manfrotto works very well for me. https://www.manfrotto.co.uk/xume

 

Ulf,

Thank you for this! Yes absolutely, I have been slightly puzzled as to why my focus was shifting in UVb. Using my Pentax UAT lens, IR is slightly in front of the UVA focal plane at high magnification. But I was puzzled as to why UVB was also infront of the UVA focal plane. But at my higher magnification the thickness will matter and my UVB filter stack is much thicker than the Baader venus filter.

 

I seem late to this party. As to CCD vs CMOS. It used to come down to quantum efficiency of the sensor. CCD used to be twice that of CMOS. But with microlenses and better chip designs, this is no longer true and CMOS sensors are better.

That being said though, a Astrophotography monochrome camera with microlenses on the sensor will be better than a sensor with them scrapped off.

Thus why I partially deam about the ZWO 1600mm sensor. It should have the best response, if you swap out the front glass with either no glass or fused silica. This anyone could do as the fron of the assembly comes off.

 

[Andrea B.]

Pentax UAT lens, IR is slightly in front of the UVA focal plane at high magnification

 

That Pentax UAT is a tiny bit pesky in IR at any magnification**. I have photos at about 10-12 feet from subject for which the IR is off when focus was made in the visible. Like I was saying above, I've had missed focus with any lens I've used so far. So I have learned to always focus through the filter in Live View while torching the subject with UV-LED (or other appropriate light).

 

OK, "torching the subject" did not come out well. How about "while shining a UV-LED flashlight upon the subject". OK.

 

Refocusing in IR is a bit easier 'cause no extra light is usually needed. I do have a little hot-shoe mounted IR-LED array in case I ever need it.

 

There are also the usual problems with focusing wide open (for more light in any wavelength) and then stopping down. None of these lenses has ever seemed to have perfect focus shift when changing apertures. This again is more apparent in close work (high mag).

 

 

 

** I still love that UAT anyway. It makes the most lovely visible photos.

[Marianne Oelund]

Not sure I can tell you why this is so, but seems to have something to do with thickness of filter and distance from subject. Like for close work (which is most of what I do), focus is often missed when using the visible method.

 

Yes, it has everything to do with filter thickness, versus depth of field (which of course is subject-distance dependent). If using a filter of fused silica, the refraction index in the UV-A band is 1.475, so the focus shifts away from the camera by about 0.325 * T, where T is the filter thickness.

 

In my case, I haven't been working at magnifications higher than 1:4, so my DOF behind the focus plane at f/4.5 with a Nikon D50 is at least a couple of mm and I only have 1mm filter thickness (Baader U). I'll never notice the 0.325mm focus shift from inserting the filter.

 

But at closest focus with the UV-Nikkor and a Nikon D610 or similar, the DOF behind the focus plane is only about 0.7mm, so if your filter thickness is more than 2mm, you would want to re-focus. Live View is a nice way to do that, but alternatively if you have a macro rail with micro-adjust, you can just move the camera back by 0.325 * T.

[Marianne Oelund]

. . . a Astrophotography monochrome camera with microlenses on the sensor will be better than a sensor with them scrapped off. Thus why I partially deam about the ZWO 1600mm sensor. It should have the best response, if you swap out the front glass with either no glass or fused silica. This anyone could do as the fron of the assembly comes off.

 

Removal of microlenses can especially be a problem with today's fine-pitch CMOS sensors which are not BSI (Back Side Illuminated). I wouldn't do a monochrome conversion with that type of sensor due to the substantial hit to QE and vignetting that can result.

 

The ZWO ASI 1600MM can be obtained for about US$1000 if you buy the non-cooled version, which is rather reasonable. Also, ZWO have adapters for camera lenses available at low cost. One drawback (for some uses, such as landscapes) is that this is only a Micro 4/3 sensor size, so a 105mm lens has the narrow field of view of a 210mm lens on a full frame camera. Also, the ADC is only 12-bit so HDR techniques are needed to realize the full dynamic range that the sensor is capable of. There is the inconvenience factor as well, as it must be tethered to a computer to work as a complete camera system.

 

Astro cameras become very expensive if you want a larger sensor. APS-H size sensors will set you back around $4K and full-frame sensors run $5-15K. Almost all of those are cooled cameras with sealed sensor chambers, so you can't change the window glass without compromising their function. I would like to have an astro camera to serve double duty in UV photography as well, but one must be careful to research the cutoff wavelength.

[dabateman]

Yes,but $1000 is still too much for me. I have actually seen the non cooled version at $800. The pro cooled version goes for $1280. I actually like the Panasonic MN34230 sensor that is in this ZWO 1600MM camera. Similar sensor to my Em1mk1. And from yesterday's test I know it can see to 280nm. But that's the limit.

With a better 302nm bulb now though I am getting reasonable exposure times. So don't need to go this way, for deep UVb.

 

Fun to remember the four variables. Light, filter, lens and camera. I now think my Camera is a good fixed factor, now with a better light. A better 300nm filter will cost me about $400. So I will hold onto its 10-12% transmission, as its IR blocked.