Using a Barrel Lens

[Two23]

I bought a gorgeous Derogy Petzval from Garett/gomules last week, and have mounted it on my Shen Hao 4x5. It's perfect! Now to use it. No shutter, obviously. Also no slot for stops. I need to get daytime exposures slow enough to count seconds. Here's what I have in mind. First, I'll order some ISO 25 b&w film from B&H. Next, I'll get some stiff black material and make some "coin" stops. These will be circular and fit snugly inside the barrel between the sets of elements. I'm thinking f16. To make, I'll measure the diameter of the tube, then divide that by two, then divide by two again and so on until I get to equivalent of f16 (lens is roughly f3.8 I think.) That will get me most of the way there but not all the way. I'm also thinking of buying a 62mm variable ND filter from B&H (2-8 stops.) I will also likely use color filters (red, orange, green, blue) on most shots as well. That will also eat up 1-3 stops. I just need to figure out how to attach filters to front of lens. I was hoping Cokin made a universal holder that would push fit onto the 61mm diameter lens hood, but can't find one. I suppose I could just hold filters in front of the lens. I'll have to think about it. I shoot at night a lot, so that right there solves a lot of problems to start with. Anyway, I love how the brass lens looks with my black & walnut Shen Hao! I might just leave it set up in my family room as a decoration, LOL.


Kent in SD

[goamules]

Glad you like the lens, it looks great on that little camera!

I've found the size of the stop can be very approximate. Because I check my actual aperture when I'm about to take the shot. I measure the actual focal length between the lens nodal point and the ground glass, after I have focused. Then I go around to the front and measure the apparent circle of light I see looking into the lens, with no film holder in place. Divide FL / Ap and you have your actual F-stop. So it really doesn't matter if you carefully measured to get exactly F11 when you cut your stop hole. It's all relative to how much focus/focal length each shot has.

Try a half inch hole at first. If you focus on something close, say you get 8 inches of FL. You'll be at F16. With slow film you'll be able to shoot in a lot of medium light just using a darkslide as a quick shutter.

[numnutz]

I was hoping Cokin made a universal holder that would push fit onto the 61mm diameter lens hood, but can't find one...

Here is a reference to a Cokin adapter for large format lenses: http://www.srb-griturn.com/cokin-uni...ptor-627-p.asp. The supplier is in the UK but you should be able to get one in the USA. The Cokin part number on the box is: Universal ring P499 maximum diameter is 80mm

nn

[Peter Gomena]

An old, cracked dark slide makes good material to recycle as a Waterhouse or coin stop. The slot in my old RR is just the right width to accommodate the thickness of a dark slide.

Peter Gomena

[DanK]

An old, cracked dark slide makes good material to recycle as a Waterhouse or coin stop. The slot in my old RR is just the right width to accommodate the thickness of a dark slide.

Peter Gomena

That's a very good idea, I wouldn't have even considered. Thanks

[Two23]

Here's what I'm thinking of doing. Buy one of those Cokin adapter rings, 60mm thread. Glue (?) it to the rear end of the lens, where it projects into the bellows. I can then use one of those 2-8 stop variable ND filters on it, and screw a color filter onto that. This puts the filter back in the dark where it's less likely to flare. Anything wrong with my plan, or is there a better one? Ring would be removeable, of course. This is a premium lens and I see myself more as the current caretaker than I do as being the owner.


Kent in SD

[DanK]

Here's what I'm thinking of doing. Buy one of those Cokin adapter rings, 60mm thread. Glue (?) it to the rear end of the lens, where it projects into the bellows. I can then use one of those 2-8 stop variable ND filters on it, and screw a color filter onto that. This puts the filter back in the dark where it's less likely to flare. Anything wrong with my plan, or is there a better one? Ring would be removeable, of course. This is a premium lens and I see myself more as the current caretaker than I do as being the owner.


Kent in SD

I'm not positive....as I've never used filters behind the lens....but, I believe adding filters to the rear can degrade the image, where if the filter is in front it is corrected through the lens...

I have a little darlot, that I can screw a step up ring into the front without the hood on....and use it for filters....slow film, shade, and 25 red filter (have yet to get a ND filter)...works well as yet...

Thanks,
Dan

[Two23]

I'm not positive....as I've never used filters behind the lens....but, I believe adding filters to the rear can degrade the image, where if the filter is in front it is corrected through the lens...

I have a little darlot, that I can screw a step up ring into the front without the hood on....and use it for filters....slow film, shade, and 25 red filter (have yet to get a ND filter)...works well as yet...

I've seen filters attached on the rear, but you may have a point about that position being far more "sensitive" than on the front of the lens, where a filter will be focussed right through.


Kent in SD

[Two23]

OK, ever have one of those times you are trying to creatively solve a problem, but nothing really good seems to come to you? And then you try to go to sleep, and just as you are getting drowsy the Big Idea comes to you? Well, that just happened to me. How do I easily attach a filter to my Derogy, without screwing it up and also making it very convenient? How about this. The lens hood is 60mm diameter. I already have a plastic lens cap coming from B&H. So, couldn't I just get a ~58mm Cokin ring adapter and some 58mm filters (red, orange, blue, green, Vari-ND), cut a 59mm hole in the lens cap, glue the 58mm adapter ring to the lens cap, and presto! I have a place to screw filters on that's quick, easy, and doesn't risk damaging the lens at all? Now, back to bed. I need to convince my wife that when I'm taking my Saturday nap I'm really thinking hard and solving big problems!


Kent in SD

[eddie]

for your aperture hole sizes you should use the square root of 2 to find your hole size. this will give you either half as much light or twice as much depending on if you divided it or multiplied it.

i make a "focal plane shutter" out of matte board. i cut a slit in it and pull it across the front of the lens. varying the slit size changes the speed with out having to vary your "pull" speed. you can get very fast speeds like this.

or just use a hat as fast as you can and under develop. works for me.

eddie