I understand this is a large format forum, but I'm sure alot people in here either shoot, or are knowledgable about medium format. I'm wondering if a 100mm enlarging lens will provide enough coverage to print 16x16 prints from a 6x6 negative. I'm using a dichro45s on a Beseler 45M frame. I'm debating between the 100mm and a standard 80mm. I was hoping for more even coverage with the 100mm, but I need to make sure I'll be able to print up to this size. Thanks!
Brian
It will surely have enough coverage, but so should the 80mm. What you should be asking about is if your enlarger has enough elevation for the print size you want!
Brian...get an 80mm or 90mm. I have a Beseler enlarger with the adjust-a-table and a 90mm APO Componon. If you plan on printing 16x16 and crop into the 6x6 image, a 100mm will not provide a large enough image on the baseboard. If you don't already have the adjust-a-table, I would consider getting one so you can blow up a smaller section to a large print. They sell used on Ebay for a reasonable price (usually around $100 tops).
80mm should be perfectly adequate.
If you have coverage and or fall off problems it could be due to using a 4x5 head for medium format. I don't know your specific enlarger but if you are just blocking light by putting only a 6x6 mask in place then you are reducing the amount of light and will get much longer print times.
My enlarger has different mixing boxes for each film format which aims to keep print times similar across different film formats.
i.e. f8 on 150mm lens will let twice as much light through than an 75mm lens at f8. Therefore unless you change the mixing box to collect the light from the 4x5 area and direct it to cover only the 6x6 area, you will get print times which are much longer.
using a 150mm lens to print 6x6 to 16x16 would require a very tall enlarger column. 80mm or 100mm lens should be fine with the correct mixing box. ( I assume your enlarger is a diffusion enlarger. If not then correct condesing lenses for your enlarging lens focal length should be used)
[pre]
Brian,
I ran a couple of formulas through a spreadsheet to compare different focal
length lenses.
Assuming you print the 56mm x 56mm image area of a 6x6 negative to 16x16",
the magnification required is 7.26 X. The formula for the negative to
easel distance is D = FL * ( 2 + M + 1/M) where FL is the lens focal
length and M is the magnification.
Focal MINIMUM carrier-easel
length distance (mm)
60 564
80 752
90 845
100 939
105 986
The maximum carrier to easel distance of my 45M is approx. 950 mm (measure yours,
and hopefully it won't hit the ceiling). Although a 90 will work, an 80 will
permit cropping.
One can solve for the maximum enlargement for a given elevation and lens focal
length. The following table assumes a maximum carrier-easel distance of 952 mm.
Focal Maximum Print
length enlargement Size
60 13.8 30.4"
80 9.8 21.6"
90 8.46 18.7"
100 7.4 16.3"
105 6.9 15.2"
The table should give you some indication of maximum print size, and the degree
of cropping which is possible.
The 60 mm lens example I've used is the 60 mm Rodagon-WA (wide angle) which
covers 6x6 and is sharp. Rodenstock also makes the 80 mm Rodagon-WA which
covers 6x9, and is nearly as good as the APO series. The 80 mm APO Rodagon N
and non-APO Rodagon N cover 6x7. The 80 mm Componon-S specs indicate that
it is designed for 6x6, not 6x7. At high magnifications, that difference
might be significant if you intend to shoot 6x7 some day.
If you intend to use the 45M for high magnifications, check the alignment
frequently... especially lensboard fit, and use a glass carrier. I prefer
my 4x5 Omegas and Laborator over the 45M for most applications.
Mike
[/pre]
If you have coverage and or fall off problems it could be due to using a 4x5 head for medium format.[...]
i.e. f8 on 150mm lens will let twice as much light through than an 75mm lens at f8.
Okay, is that some strange physics to celebrate Halloween? Or am I a victim of acid fixer fumes?
Ill grant you that it wasn't the best explanation ever given but that doesn't mean you aren't an acid fume victim. Technically the statement is correct. Don't you think 150mm lens at f8 lets through twice as much light as a 75mm lens at f8 ? All other things being equal of course.
I'm tired. I couldn' tell you for certain I've even awake.
What you are relating must have something to do with a mixing chamber. Lemmie sleep on it. I'll probably forget by the morning anyway.
rob wrote "ll grant you that it wasn't the best explanation ever given but that doesn't mean you aren't an acid fume victim. Technically the statement is correct. Don't you think 150mm lens at f8 lets through twice as much light as a 75mm lens at f8 ? All other things being equal of course."
If you're trying to tell me that I should use twice as long a shutter speed, other things equal, at f/8 with a 150 as with a 75, to get proper exposure, you're demented. Other things include magnification and advice from a light meter reading incident.
To be nicer, this is not the standard result, please explain further.
If that's not what you meant, again, please explain further.
for a 150mm at f8 lens the physical aperture area is 58.90 square mm
for a 75mm at f8 lens the physical aperture area is 29.45 square mm
i.e. the 75mm lens aperture lets half as much light through at f8.
Your mistake is that you are thinking in terms of a normal taking lens usage where because of the focal length of 150mm being twice as much as 75mm lens, the light fall off due to inverse square law results in same exposure for film for both lenses at f8.
If you had read my original response and paid attention to the context in which it was written, which is comparing large format to medium format in an enlarger( where the subject is the negative) then what I said applies.
take a 90mm x 90mm area from a 4x5 neg and enlarge it to 16x16 inches using a 150mm lens. The subject(negative) is 183mm from the lens whereas the image distance(print) is 827mm.
then take a 56mm x 56mm neg and enlarge it to 16x16 inches using a 75mm lens. The subject distance(neg) is 85.33mm from the lens whereas the image distance(print) is 619.3mm.
Although the focal length of the 75mm lens is only half of the 150mm we have to use a different maginification for the 16x16 print and so the image distance is not half that of the 150mm lens.
Therefore the fact that a 75mm lens only transmits half the light of a 150mm lens at f8 comes into play. That is why the correct mixing box is important unless you want really long print times.
You could argue that the difference is becuase of different magnification but my statement that a 150mm lens at f8 lets through twice as much light a 75mm lens at f8 holds true which equals that it is you who is demented.
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