Topic: do we do technical here?

[Ken B: eyes, I just do eyes.]

I have a Pentax 67 with a 135mm macro lens with the Pentax 67 bellows.

I have the bellows set to about 320mm from the film plane to the rear lens element

I calculate a BEF of about 5.62 or a light compensation of around 2 1/3 to 2 2/3.

I have just shot a roll of FP4 rated at 100 ISO then rated the lightmeter to 20 ISO to allow for BEF

Does anyone see a hole in this so far?

I did this stuff at college about15 years ago and then bought cameras that sorted it out for me.

I think someone said something about Karma and I wanted to know if that was 120 or large format camera system - they just walked away.

[This-is-damion]

yes we do technical......not sure i do.

Although  i do recall looking at exposure compenstion for LF stuff.

I have to duck into  a meeting.......do a quick search of the forum, if not ill try and find when i get back,   someone pointed me to a great youtube video of easy way to sort it.

a website has a printable circle thing and ruler you use.   very simple concept, easy to use - im guessing it would apply to this as well.....but i could be very wrong!!!

[Pete_R]

All looks sound to me. But a BEF of 5.62 is nearer 2 1/3 than 2 2/3 stops.

[Francois]

a website has a printable circle thing and ruler you use.   very simple concept, easy to use - im guessing it would apply to this as well.....but i could be very wrong!!!

This is the Quick Disk
It probably would work but you'd have to remove the viewfinder in order to get the ruler next to the ground glass...

Ken, your problem got me scratching my head thinking "I've never calculated such a thing". So I went around the internet to pick up a few formulas. I also hacked a few myself and came up with the following:

Focal: 135mm
Bellows: 320mm
Film: 100 ISO
Compensation: 5.62x
Compensation in f/stops: 2.49
Compensation in EI: 17

Does that sound right? I can post the formulas I used to compare...

[Pete_R]

Thought I'd revisit this as it's been a while and it looked like Francois got a different answer to me. In fact he's correct. The factor based on your figures is 2.49 stops.

However, I'm not sure your method of measuring the extension is correct. I think I'm right in saying it should be measured from the film plane to the rear nodal point of the lens and without knowing where that is, it's not possible to just measure the extension. There's various ways suggested to get around this but I think Ansel Adams' is the simplest which is to measure the amount the lens has moved and add the focal length. So, measure from the camera lens mount to the back of the lens (or the actual length of your bellows) and then add 135mm. Probably not a lot in it though.

[Ken B: eyes, I just do eyes.]

okay I went ahead and did it. Shot a closeup of some medical pincer things.

did an incident reading at f8, so decided to start there and bracket @ 1/2 stops down to f4 which is the best the lens will do.

I am using some softboxes as constant light because the camera body won't fire the flash, so my shutter speed is 1 second    Who can spell "Mirror slap" kids - or should I say visual mirror slap    anyway this run is more technical glitch sorting than anything else.

I have been doing this at work, just flitting by on my way past or while waiting for the computer to do something. I cleaned the darkroom yesterday in anticipation of doing some "shake and bake" with my new dev tank, I even managed to score an apron to put over my work clothes.

I have just gone to check the shutter speed setting as I couldn't remember it for this post and when I looked at the camera body I have forgotten to take it off "X"  so I will have to start again.

excuse me for a moment - aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaarrrrrrrrrrrrrrrrrrrrrgh!!!!!!!

I'm better now, well back to the studio at lunchtime

[Ken B: eyes, I just do eyes.]

it seems we have consensus on BEF I am going to spend sometime today to looking into the practical application of the BEF back into ones technique and workflow, for example I rated the lightmeter down to ISO 20, I want to work that out to see if that was the golden move or there is a better way.

open to suggestions BTW.

And thanks to you all for you thoughts and input so far.

[Francois]

Isn't there a scale on the rack & pinion for the bellows?

As far as the nodal point thing, I figure it potentially wouldn't have that great an effect if its short enough...

[Ken B: eyes, I just do eyes.]

Isn't there a scale on the rack & pinion for the bellows?

There is but it is for a 105mm lens

[Francois]

I looked through a book on optics. The answer is:
Bellows extension - lens focal length = focusing travel

[Pete_R]

Bellows extension - lens focal length = focusing travel

...or Bellows Extension = focusing travel + lens focal length

which is Adams' method.

[db]

...or Bellows Extension = focusing travel + lens focal length

which is Adams' method.

Probably a lot more reliable than Don's method:
1. crank out the bellows 'till it's in focus
2. say "geez, that's getting out there- I'd better open up a couple of stops''
3. Bracket exposures.
 
You you can tell why I never became a scientific photographer...

[Ken B: eyes, I just do eyes.]

...or Bellows Extension = focusing travel + lens focal length

which is Adams' method.

Probably a lot more reliable than Don's method:
1. crank out the bellows 'till it's in focus
2. say "geez, that's getting out there- I'd better open up a couple of stops''
3. Bracket exposures.
 
You you can tell why I never became a scientific photographer...

So is this same method applied with when using your new 5x4? mmmmmmmmmmmmm? Be truthful young man.

[Ken B: eyes, I just do eyes.]

You you can tell why I never became a scientific photographer...

I can just see it now:  "Don could you take some views of this persons skin lesions - and NOT with the bloody Diana this time!!"

cheers

[db]

So is this same method applied with when using your new 5x4? mmmmmmmmmmmmm? Be truthful young man.

Nah, you're right. Scratch #3.
I'd open up a couple, and be bloody cocky enough to reckon I'm close enough the first time.

Oh, and with trannie I would be scientific enough to process the first before I push-pull the remainder. I might be an exposure cowboy, but I'm not that crazy

[Ken B: eyes, I just do eyes.]

Oh, and with trannie I would be scientific enough to process the first before I push-pull the remainder. I might be an exposure cowboy, but I'm not that crazy

Not that crazy, mmmmmmmmmmmm let me get back to you on that one.

As for trannie, I have never been so totally absorbed in a stream of photography where I was using trannie so much that clip testing or push-pulling became part of the workflow.

I have always used 100ISO trannie in my Nikon and it seemed to render pretty accurate and consistent exposures.

Not being in a studio often, I didn't have much call for medium or large format trannie use, I used these 2 formats but mostly B and W or Colour neg.

So trust me Don, if I start shooting more medium format trannie, well best have your laptop with you and be near a free wifi zone to give live chat advice on the fly.

cheers