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Forum: Photographic Technique
05-02-2015, 11:40 AM
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From your equipment choices above it would seem you are working on a practically a non-existent budget. If we had an idea of what your budget is would help on recommendations.
Do the images between specimen have to reflect relative size (i.e. shot at the same magnification) or will a scale be provided and differing magnifications can be used on a per subject basis?
How cramped is the work area where you will be photographing the specimens? Longer focal lengths give you more working distance between the front of the lens and the subject. This make lighting easier but can be a problem in cramped quarters.
How much magnification is needed? Consider the dimensions of the APS-C (crop) sensor in Pentax cameras is usually listed as 23.5 × 15.7mm.
So at 1x magnification a 15mm long/wide object would take up ~64% of the length of the sensor. A 5mm long object only ~21%.
At 2x magnification the 5mm object would take about 43%
Looking at the manual for the Pentax Auto Bellow-A (all lenses set to infinity):
for the Pentax M-50mm and A-50mm f/1.7 lenses (non-reversed)
values magnification, extension (mm), working distance (mm)
0.8, 42, 93
1.0, 52, 80
The same lenses reversed
1.0, 61, 90
2.0, 113, 64
3.0, 165, 56
M-Macro 100mm f/4 (non-reversed)
0.4, 40, 340
0.5, 50, 290
0.8, 80, 215
1.0, 100, 190
reversed - not given, not recommended.
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Forum: Photographic Technique
05-01-2015, 07:17 PM
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See the post linked below on some of the magnification ratios on reverse mounted lens without lens stacking or tubes. This is only effective on lenses with a focal length less than 50mm, With 50mm lenses or longer you should reverse them (on extension tubes or bellows, not lens stacking) with greater than 1x magnification. Refer to he Pentax Auto Bellows K, M and A manuals which give the reason for this and I'm to lazy to find my earlier posts on this.
https://www.pentaxforums.com/forums/22-pentax-camera-field-accessories/287960...ml#post3155624 |
