24" Red Dot Artar Vignette Question...

[Dan Quan]

I just received a 24" Red Dot Artar I won on that auction site and it's mounted to about a 3.5" barrel with ~ a 4"x4" plate, like an extended lens board. I figure there would be no problem with 4x5 film, but I want to use it with 8x10. Without buying a lensboard for this setup is there a way I can figure out whether or not this will vignette with 8x10 at infinity? For an extra 3" of bellows draw I definitely want to use it this way if it's practicable. Thanks.

This is a link to the listing with photos.

 

[Dan Fromm]

Dan, I use a lot of lenses hung out in front of a shutter, sometimes far out in front. I use a simple similar triangles model to tell in advance whether vignetting will be a bad problem. It is highly approximate, sometimes says that setups that work shouldn't, so use it with care.

In your case, my little model comes down to: if [obstruction's diameter/2]/[distance from the lens' diaphragm to the obstruction (in your case the rear of the tube)] > [(format's diagonal/2)/lens' focal length], vignetting at infinity shouldn't be a problem as long as the lens is centered on the film. I think you're home free but since I'm guessing at the dimensions I could be mistaken.

What I don't see is how you can avoid buying a board anyway unless the tube behind the lens is on a plate that fits your camera.

I'm not sure what you'll do for a shutter, either. SKGrimes makes some recommendations ...

 

[Dan Quan]

Thanks for the info Dan, I will be buying a board from zbima1 on ebay like i always do, he is just fantastic at making beautiful boards fast. But I didn't want to spend $35 and find it doesn't work for me, then need to buy another drilled differently. As for a shutter, I'll use a lens cap for now.

 

[Dan Quan]

Well, I got this thing all cleaned up and it turned out to be a really good deal on a long lens. I am quite pleased.

 

[brofkand]

I will be buying a board from zbima1 on ebay like i always do, he is just fantastic at making beautiful boards fast.

Thanks for that recommendation. I just ordered 2 boards from him for my Calumet 4x5. $10 each is a fantastic price, cheaper than used boards!

 

[Dan Quan]

The guy is is like a real find, right!? He's easy to work with, makes beautiful boards and his prices are great, what more is there?

 

[Dan Quan]

I finally got it all together and it focuses for a head & shoulders shot easily with full draw at about 6 feet and a full length at about 20 feet. I am so stoked!

I haven't tried it at infinity yet but, since it's really for people I tried it at about 30+ meters and it looked good so I'm not worried. Thanks for the formula and help Dan Fromm.