Home made hobo 10x8 camera + componon

[paulie]

here is a link to a shot i made today on my hobo camera, i seem to have a hotspot under the light in the picture

the light was on in the daytime so i was hoping to get your opinions on what this hotspot might be

is it a lens issue or perhaps flare

the lens is a componon 210mm f5.6 in a compur shutter.

 

[Ian Grant]

and the link is ?

Ian

 

[paulie]

here it is

 

[Ian Grant]

looks like flare from an uncoated lens, you certainly don't need a centre filter

My Componon 210 won't quite cover 10x8 on my enlarger so would be worse at Infinity, so you must be lucky.

Ian

 

[ic-racer]

Light leak? though a little unnusual for it to hit right in the center like that. How is the lens attached? Do you have a ground glass back? If it is flare you can see it on the ground glass.

If it is flare, you can also consider a modern multicoated Symmar-S 210. They are way-cheap and would have a similar coverage suited to that type of camera.

 

[paulie]

yeah i was most surprised when it actually covered 10x8 at infinity, i will post a picture of my camera at some point for you to look at.

no ground glass just exterior site lines, calumet lens board was used with compur and elements screwed directly to shutter

the lens board is press fit in a rebated opening in the camera and then black tape sealed, the camera has been light tested with paper for 4 hours with no noticable fogging

flare could be a factor , i had a u.v filter on the lens with no hood , naughty me, but it was a shady shot

 

[paulie]

the box is a kinda fair weather tripod, going to be used for ALT process

 

[vdoak]

Does a blade on the shutter hang open? On one of mine the lubicant turned to thick paste that stopped the shutter form closing completly and in sync. One blade "hung open" a slpit second longer than the others. This left an over exposed area dead center when it happened but it did not happen all the time.

 

[Marco B]

Does a blade on the shutter hang open? On one of mine the lubicant turned to thick paste that stopped the shutter form closing completly and in sync. One blade "hung open" a slpit second longer than the others. This left an over exposed area dead center when it happened but it did not happen all the time.

Funny, I have never experienced this, but I was starting to think along the same lines, because looking at the image, is flare likely? It seems to have been an overcast day in Amsterdam when this picture was taken. There are hardly any shadows.

 

[paulie]

i used a 6 second exposure on a test sheet of paper and the problem is there still, ive removed the filter and attached a hood, no change in hot spot

so i dont think it can be shutter blade problem

it seem to get worse as the lens gets stopped down

f11 is ok f22 hotspot

 

[unclemack]

Hi Paulie,

Do you still have the original mount for the Componon? If the flange-to-flange distance between the front and rear capsules of the lens is incorrect it may explain the hotspot and the overall softness that I think I can see?

There's probably someone here who would know without even checking - but it's not me!

 

[paulie]

yes i have checked the overall spacing against the original mount and they are very close perhaps .2mm difference, would this be enough to create this hotspot?

i am very close to mounting my pinhole now and ditching the lens which would be a shame as the camera i have built is really a little complex for just a pinhole

plus i already have a wide angle 10 x 8 pinhole

any suggestions for a 210mm (compur 1) that will cover my film and will fit in with my tiny budget?

 

[erikg]

I had a similar issue with a pinhole type crack in a lensboard. Drove me nuts, but a buddy helped track down the problem. So I think Victor might be on to something about the shutter. It may be hanging up, and that could happen inconsistently, so testing may not catch it at first. Maybe it only happens at slower speeds. We had a shutter like that in the studio, but it didn't matter there because we shot with strobes. It wouldn't take much, a tiny crack that wouldn't be so obvious.

 

[paulie]

i use the same lens board with another lens and have no issues, it is definitely a lens issue i think, my final test tomorrow will be to unscrew the front element a turn or two ,if this doesnt help then the lens will be retired i think

my shutter speed is generally long over a minute , therefore shutter hang isnt a issue, and i know the shutter is reliable as i use it for other lenses with no ill effect

 

[erikg]

The shutter hang up would be between exposures, where it is not closing all of the way all of the time, so that you are getting a small amount of additional exposure.

 

[paulie]

i will try another of my shutters and get back to you on this, generally i lens cap after a exposure as it is a one shot machine

oops i forgot i have tried this already ( tried different shutter) with no change to the hot spot

i just think enlarger lenses are a no go for regular shooting

 

[paulie]

one weird thing i have noticed is that this 210mm lens is actuall focusing at infinity at roughly 205mm and not 210mm

any thoughts here?

 

[erikg]

Actual focal length rarely matches the marked focal length exactly, nothing too strange there. There isn't anything wrong with using enlarging lenses for shooting as such, pretty common for close up work. Hope you can figure it out, it looks like a pretty neat camera.

 

[paulie]

thanks for your help

i will test the lens spacing i think then i will rest :0)

 

[Toffle]

thanks for your help

i will test the lens spacing i think then i will rest :0)

You could also test it as a convertable... try a shot with just the front or the rear elements. Your focal length and aperture will need to be recalculated, but it might help isolate the problem.

 

[paulie]

yeah ive used the lenses rear element reversed before and it worked well,around 350mm at f13, no hot spot, sharp in the center soft around the edges on a 4x5 view camera

unfortunately the extra focal length would warrant a complete new design and construction of my hobo

little disappointing, but i will live

 

[Toffle]

yeah ive used the lenses rear element reversed before and it worked well,around 350mm at f13, no hot spot, sharp in the center soft around the edges on a 4x5 view camera

unfortunately the extra focal length would warrant a complete new design and construction of my hobo

little disappointing, but i will live

The other option is to put it in a box and send it to me... That's the kind of stuff I love to mess with.

 

[paulie]

haha i think ill keep it for the rear cell reversed, thats a good combo anyways, i am going to test it one more time , if its no good i will revert to my 250mm pinhole

 

[paulie]

i today tested the lens reversed on a calumet and this has corrected the hotspot,great but how do i trigger the shutter, well...

my hobo camera is foam core so i just made a hole and pushed a shutter relaese through and glued it firmly with epoxy resin and graphite/Indian ink to light proof it

this now allows me to preset the shutter and aperture (thats no problem), i lock the shutter release to prevent accidental firing.

here is a shot i took tonight

1.5 hours f22 view from my balcony ,jordaan amsterdam

thanx for your help

i also have picked a couple repromaster lenses to play with

lucky me :0)

 

[paulie]