Recent purchases

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ray_parkhurst
Posts: 2963
Joined: Sat Nov 20, 2010 10:40 am
Location: Santa Clara, CA, USA
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Recent purchases

Post by ray_parkhurst »

Many of you know I finally purchased, and kept, an A7Rm4 recently. I have been using it exclusively for a few months now for my coin photography. I should probably start a thread regarding my various findings so far, as well as the related evaluations of various lenses I had been using on my HRT2i. Bottom line is some lenses work well, and others not so well. This was expected, but there were some surprises. After a few more evals I will likely write a summary thread for interested folks.

I was lucky on a couple of recent auctions. Most recently, I picked up a Computar dL 50-80mm Vari-Focus enlarger lens. I have not tested it yet, but I was compelled to buy it based on a simple calculation of the magnification zoom range it might offer. With 100mm total extension, it should give m=0.25x at 80mm and m=1x at 50mm. This is overly simplistic of course, and needs to be verified experimentally, but that is an excellent range for coins, and I just had to buy the lens. Probably worth another thread once I do some evaluation.

Another lucky auction left me with a good quantity of idler rails made by HiWin and Nippon Bearing. I will create a trading post ad so as not to discuss commercial items here, so interested folks please take a look there.

The P. Angenieux G=12/6 lens I discussed in another thread is working very well on the A7Rm4, though it won't replace the 95mm Printing-Nikkor. I'm not sure anything can.

Another lucky auction win was for a manual 6"x6" Parker XY table. It is heavy, and listed shipping was exhorbitant, but the seller lived just a few miles from me, so I had the advantage of being able to do local pickup. It replaced my automated XY table used for the 2x3 tile panoramas with the HRT2i, and now I am doing simple 1x2 tile panos with the A7Rm4. The 1x2 panos don't require precision movements, so manual operation works well. I end up with ~9000x9000 final image size, just shy of the 9600x9600 I got with the HRT2i, with far less work, and fewer lighting issues due to the lower magnification (~1.7x vs 2.0x) giving greater working distance.

I also picked up a M42-M42 adjustable iris aperture. I'm wondering if it can help with reflection issues by inserting it into the optical path. I'm not sure if I will mitigate or exacerbate the issues, but that will be an experiment.

Edited to add: something that may interest those of you who are nearsighted. I've always had reservations about going to optometrists, as they have never been flexible in slightly weakening my distance prescription to give a more overall usable prescription. As I age my eyesight has gradually improved, and prescriptions that optimize distance vision don't last very long. I was tired of paying hundreds of dollars for glasses that may only last a year, at best two. It seems the optometrists in the US have a monopoly on eyeglasses, at least for us nearsighted folk. Farsighted folk can buy reading glasses, but you can't go to a CVS and buy distance glasses. However, I discovered that indeed they are available on eBay, both from US and Chinese sellers. I now have a full range of eyeglasses, from distance down to computer, and paid less for all of them than I would have for a single pair had I gone to the optometrist. Just a tip for fellow nearsighteds.

ray_parkhurst
Posts: 2963
Joined: Sat Nov 20, 2010 10:40 am
Location: Santa Clara, CA, USA
Contact:

Re: Recent purchases

Post by ray_parkhurst »

I have done some testing on the Computar dL 50-80mm Vari-Focus lens, with mixed results...

The lens is very sharp, with minimal CAs across the whole zoom range. This was unexpected given results I've seen on other Computar lenses, so good so far...

But unfortunately the "zoom" function worked opposite what I expected. Normally, zoom lenses are shortest at or near their minimum FL, and longest at maximum FL, but this lens is the opposite, ie shortest at 80mm, longest at 50mm. This has the effect of amplifying the WD difference between the min and max FL, ie making it very non-parfocal, with the result that at 50mm and 1:1 the WD is only ~40mm. This is too short for effective illumination for small coins like Cents.

It's too bad, as this lens is otherwise very good.

ray_parkhurst
Posts: 2963
Joined: Sat Nov 20, 2010 10:40 am
Location: Santa Clara, CA, USA
Contact:

Re: Recent purchases

Post by ray_parkhurst »

Another recent purchase was a Canon 35MP, the RMS threaded 35mm Macrophoto lens. This lens is a strong performer and I've often wondered how it would do at lower magnifications, though I have never been able to try it in my previous system due to long minimum bellows length and long camera register distance. The combo kept me from achieving less than 2.4x magnification. Well, I have now rebuilt my system, with a Vivitar bellows modified to mount an E-mount bayonet directly to the camera standard (after milling some extension from the standard). This reduced the minimum extension, and combined with the short E-mount register of the A7Rm4, I can achieve ~1:1 with the 35MP. Unfortunately, it can't cover the FF sensor at 1:1, but it does cover the sensor height, so is capable of framing a Cent very nicely.

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