Infinity objective on telephotos

[ChrisR]

It would have been nice to have done a "proper" test, but I lack the space .
This is with a 24 x 36 sensor.
Enough adapters arrived to try a Nikon 10x 0.25 infinity objective on a couple of lenses which haven't been tried here yet, I believe:

A) Sigma 28 - 300mm SD zoom, a few years old
B) Sigma 400mm f/5.6 Apo, 10(?) years old
C) Nikon 80 - 200 f/4.5 zoom. That's the one which Ken Rockwell likes, the latest of the versions with the rectangular mask at the back. A very sharp lens.
D) Nikon 70 - 210 f/4 zoom. 25 years old. Quite a good performer in the field, unusual in that the front element rotates and extends with focus.

I was only able to fire some shots hand-held, "catching" something sharp when I was lucky, then expanding the view (x27) on the camera. But experience suggests that's not unreasonable.

A) and C) looked fine at the tele end but both vignetted as soon as the focal length was shortened from their maxima. I thought the super-zoom might be awful, but didn't see that.

D) had sllight cutoff at the corners of the frame even at the long end, with some softening of the image near the edge, but I think it would cover a smaller format well enough.

B) Looked very good, covering the frame evenly, and giving me 20x magnifaction. But it's a bit hard to hand-hold half a yard of camera on a 1.8mm field of view. I expect Brian could manage though

[Bob^3]

Chris, thanks for the additional data points!

I’ve also been trying to find a reasonably compact zoom lens in this zoom range for use with the Nikon CFI 10x 0.25 NA objective on the full frame D700. It would seem that a 100-300mm or 100-400mm zoom would be ideal for this purpose. Unfortunately, tests with my one zoom in this range (Nikkor 75-300mm f4.5-5.6) showed severe vignetting even at 300mm, wide open. I’m not sure it would even cover a APS-C crop sensor at 300mm. Since I no longer use this lens for general photography, I'm considering disassembling it to strip out the aperture and any other limiting baffles.

I’ve been trying to find a way to predict whether a particular inexpensive zoom will function well throughout its range in this application. It seems clear that any vignetting that occurs with the lenses I’ve tested so far is mostly due to hard physical vignetting where the objective acts like a pinhole causing a shadow of the aperture blades to be projected onto the corners of the sensor; the size of the shadow varies in direct proportion to the aperture size. So I would guess that the larger maximum aperture zooms would be more likely to work well---but of course, these would also tend to be both more expensive and heaver/bulkier lenses. Perhaps more important than max aperture is the relative size and position of the entrance pupil. Looking at the prime lenses I’ve tested, there does appear to be a correlation with this. The 105mm/4 AI (which performs well as a tube lens) has a large apparent entrance pupil (25mm at f/4, measuring diameter at arms length). And the entrance pupil appears to be very close to the front of the lens, while with the 75-300mm AF zoom the entrance pupil appears smaller (18mm at max aperture, about f/4.5) and much further recessed toward the back of the lens, when set to 100mm zoom.

Unfortunately, these parameters are not typically provided by lens manufacturers; so it’s pretty much a case of try it and see. I think I’ll go on a tour of local used camera shops with my CFI 10x and some step down rings and gather some more data points!

[Craig Gerard]

Reading with interest.

Keep us updated.

I've posted this in another thread; but it probably belongs here too.

In regard to the Canon EF 70-200MM f/4 L USM.

Pau's observations using his IS version are spot-on. I'm observing the same results with the non IS version of the Canon EF 70-200mm f/4 L USM on the Canon 50D (APS-C, 1.6x crop factor)

It delivers (aprox) 10X at 200mm and 6.9X at 150mm and 5.62 at 135mm, focused to infinity.
Resolution and illumination are even up to 150mm, at 140mm there is some vignette but very usable for centered subjects when corners are no critical.

http://www.photomacrography.net/forum/v ... hp?t=10821


Craig

[ChrisLilley]

I’ve also been trying to find a reasonably compact zoom lens in this zoom range for use with the Nikon CFI 10x 0.25 NA objective on the full frame D700. It would seem that a 100-300mm or 100-400mm zoom would be ideal for this purpose.

I think I’ll go on a tour of local used camera shops with my CFI 10x and some step down rings and gather some more data points!

Not especially compact with its 95mm front filter thread, but may be available in a used camera shop: Nikkor Zoom 50-300mm f/4.5

[ChrisR]

There's a nice 200 - 400mm f/4..!
I've looked into those zooms again to see if I can see a difference which accounts for the 70 - 210 not being good. Not really. It's possible that the entrance pupil is nearer the camera than the exit pupil, but it's not immediately clear.

For covering the 24 x 36 fame, I think a teleconverter could be an answer. Using a higher NA objective (10x 0.45) should provide more detail, but I can't really see much difference. One possible reason for that is that I'm hitting the limit of the sensor pixels (8 micron) . So I'm thinking that expanding the middle of the image could fill the frame, and give more magnification with more detail in the image.
If the 10x 0.25 and 10x 0.30 are already beating it, then it would become normal procedure.

It would be interesting to try extending the telephoto, whether by internal focus, or extension tubes. That does mean that the "infinity" objective is being asked to focus beyond infinity, if I have the ray-path correct. Probably not a good thing, but needs testing.

[Craig Gerard]

Something like this would be interesting to use on appropriate/compatible Canon lenses.

http://www.the-digital-picture.com/revi ... eview.aspx

Something lost, something gained....

If anyone has the 'bits' I'd be interested in hearing a report.

Craig

[ChrisLilley]

I expect that I will try one of these newfangled infinity lenses at some point. When I do, I have several options for Nikon-mount 200-ish mm lenses. In order of predicted performance (guestimate best lens first):

• * Voigtländer APO-Lanthar 180mm f/4
  * Nikkor 180mm f/2.8 ED AIS
  * Zoom-Nikkor 80-200mm f/4 AIS
  * Арсенал ТЕЛЕАР-Н 200mm f/3.5 (Arsenal Telear-N)

The APO-Lanthar has a 49mm thread, so a 49-52mm step-up is indicated. The 180ED has an inconveniently large 72mm. The Ukranian lens has an undesirable yellowish-green tint and so requires a custom white balance.

[Bob^3]

Not especially compact with its 95mm front filter thread, but may be available in a used camera shop: Nikkor Zoom 50-300mm f/4.5

There's a nice 200 - 400mm f/4..!

Gee…thanks for the suggestions guys. But my primary goal for this combination is for portable field use. Come to think of it, I also have a Nikon 300mm f/4 AF-S and a 500mm f/4P that I haven’t tried with the 10x/0.25 CFI yet. It might be worth it though just to see the strange looks from fellow photographers when they see me with the 500/4 mounted on a heavy tripod with a Wimberly head pointed at some tiny subject 10mm away, with the “lens cap on”!

For covering the 24 x 36 fame, I think a teleconverter could be an answer. Using a higher NA objective (10x 0.45) should provide more detail, but I can't really see much difference. One possible reason for that is that I'm hitting the limit of the sensor pixels (8 micron) . So I'm thinking that expanding the middle of the image could fill the frame, and give more magnification with more detail in the image.
If the 10x 0.25 and 10x 0.30 are already beating it, then it would become normal procedure.

Yeah, teleconverters are also on my list of tests. And I agree, the 8.45 micron pixel pitch of D700 may be helping improve apparent resolution results, with the trade-off of needing a larger image circle at lower magnifications.

It would be interesting to try extending the telephoto, whether by internal focus, or extension tubes. That does mean that the "infinity" objective is being asked to focus beyond infinity, if I have the ray-path correct. Probably not a good thing, but needs testing.

I’ve tried this with certain prime lenses:

http://www.photomacrography.net/forum/v ... ht=cfi+10x

I should clarify my previous observations regarding focusing the base lens closer than infinity. It does seem to work well with limited extension. On the Nikkor 105mm/4 AI, the corner vignetting improves to software correctable levels at about 5.5x (helicoid focused at 20 feet) and the corner sharpness improves (but is still somewhat less sharp than the center). The center sharpness does not appear to degrade with this degree of extension on the full frame D700. As the focus is racked out closer to max magnification (½ life size for this lens), the corners develop definite softness and significant blue-yellow CA.

The other primes (Nikkor-Q 135mm/2.8 AI and 200mm/4 AI) show similar behavior as the helicoid is racked out.

For new members, it is important to note once again that these are my subjective observations based on relative comparisons only between these exact lens combinations. As with all such observations, they should be viewed with a healthy dose of skepticism until proper tests are performed and posted that include head-to-head comparisons with known lenses as controls such as the Nikon CF finite series. This should give a better estimation of true performance.

[ChrisLilley]

Come to think of it, I also have a Nikon 300mm f/4 AF-S and a 500mm f/4P that I haven’t tried with the 10x/0.25 CFI yet. It might be worth it though just to see the strange looks from fellow photographers when they see me with the 500/4 mounted on a heavy tripod with a Wimberly head pointed at some tiny subject 10mm away, with the “lens cap on”!

Thanks for that image, which made my day start with a big grin.

[ChrisR]

I’ve tried this with certain prime lenses:

So you did, sorry, it's hard to read everything and remember.

I suppose if a 500 f/4 is a bit big you could try a 500m mirror lens?