A 19" RD Artar and a top hat to extend it 2 or 3 inches?
A 19" RD Artar and a top hat to extend it 2 or 3 inches?
"Landscapes exist in the material world yet soar in the realms of the spirit..." Tsung Ping, 5th Century China
Well, since all of this took place, I had opportunity to pick up a 16 1/2 RD Artar in primo condition mounted in a Copal #3 (803,000 ser. no. range). I have tried focusing it at infinity and coverage seems to be good, even at only f/11 or so. (The very coarse ground glass is a real pain for getting perfect focus nailed. Will be looking in to getting the ground glass replaced pretty soon.) Being the cautious type, with the cutouts that the ground glass has in the corners, there has got to be some quick way to check to ensure that we're not looking at any real drop off there. The level of illumination on the left and right sides of the ground glass don't show much drop off, so I am optimistic that the corners will be covered well. That said, are there any suggestions for a quick and simple way for checking those areas to ensure that we do indeed have full coverage? I'm looking to get this done in the next day or so in order to be able to return the lens if it turns out to be short. I'm sure that there's some simple way to do this that I am overlooking. (Hey, it's Monday!)
Thanks,
Ed
I gave the dilemma in my previous post some further thought, and figured out a good way to get this addressed. I purchased some frosted plastic report covers from my local office supply store, and cut out some 2 inch squares. Those were taped in to diagonally opposite corners. I figured that they would give me some means of focusing, and they did. So, even at f/11 (Sinar lensboard adapter for Technika lenboards blocks the aperture control from opening up all the way. Annoying.....), I have coverage in the corners. Sharp coverage, not just illumination! Very pleased to be able to confirm this, and to share a way to be able to check the far corners when faced with a ground glass that has the corners clipped. Now time to get out the 210mm Computar and check that one out.
FWIW,
Ed
Film does not see light in the same way as the human eye. What appears to be illuminated to the human eye on the GG will not be the way film sees the same light via the lens. Only way to really know is test using film. As for image circle, RDA has a larger circle of illumination than circle of specified performance definition. Many decades ago used a 6" RDA on 4x5 at infinity, it "covered" but the optical performance at the edges of the 4x5 sheet was sort of OK only. Since then this 6" RDA as been relegated to 6x9 roll film where it does good.
Bernice
Thanks for the comments, Bernice. I understand that film will not react the same way to light as our eyes will. I also understand that the circle of illumination is always larger than the actual image circle. That said, what I was able to do in the far corners was to get a crisp image which was checked with a 5x loupe. I had thought that if I were only to get those corners illuminated, then we would only have a hazy image of some sort, or even just some stray light falling in the corners, rather than a clearly identifiable and sharp image. Perhaps I'm not understanding something here. If so, your comments or those of others are welcome.
Thanks,
Ed
Started using a 19" RDA as a tele on 5x7 decades ago, recently added a 16-1/2" RDA as an alternative 5x7 tele, makes really GOOD images on 5x7. They should both cover 8x10. Knowing both works for 7x17 is good.
Bernice
Just as a belated follow up to this old thread, I wanted to mention that some test photos taken with the 16 1/2" RDA worked out well. The coverage on the negative is corner to corner. This confirms what I did on a much more crude basis as discussed earlier in this discussion.
Thanks again to all who contributed!
Ed
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