Incidence metering with macro photography

ksklo

Well-Known Member
I have recently bought the 120/4 Makro Planar for my Contax 645. In the past I had only limited experience with macro photography and I was mainly using Canon's 100/2.8 macro lens. Now with the excellent MP, I am excited to test out its macro capabilities and performance.

While I rely on handheld incidence lightmeter heavily most of the time, I did the same naturally this past weekend when I visited the annual Flower Show in Hong Kong. I brought along two cameras for different purposes. The RX II with VS 80-200/4 zoom with extension tubes as well as the Contax 645 and MP 120 for close up were my main setup.

Once again I used my Sekonic lightmeter to measure the light levels and inputed the desired exposure readings manually on both cameras. I shot slides (provia on RXII and velvia on 645), and it turned out that the slides on the RXII had right on exposures but all the closely zoomed in C645 shots were heavily underexposed, at least 2-3 stops. Interestingly enough, when the MP was used to take normal shots nand ot as macro, the incidence meter readings were also spot on.

After seeing the developed slides I tested the TTL metering with the MP mounted on my 645. I further discovered that at minimum focusing distance the MP would require almost an additional two stops of light as compared to when the lens was focused at infinity!

Has anybody noticed this before? And how would I be able to use a handheld incidence lightmeter effectively with this lens? By the way, when I shoot macro on slides, I would try to avoid using the in camera meter because I could afford little room for exposure errors with slides.
 
S

ssv31

Well, apart from measuring the subject brightness with the internal meter, I see two options:
1) using a grey card + internal meter;
2) measuring with the incident meter and correcting the exposure depending on the scale/focusing distance. In this case you should measure the correction once and make some kind of handy table or plot to simplify your field work.

I would choose the first option.

Regards, Sergei.
 

kaare

Member
Ken,
This is an absolutely normal and well known phenomonen - especially to those working with large format cameras: With long extensions you have to compensate your exposure reading if you do not use the TTL meter in the camera.

You should be able to find tables with the factors you have to compensate with at a given magnification ratio.

Your APO Macro Planar will show you the magnification ratio on the lens barrel when you extend it, so all you have to do is to look in the table at the given magnification ratio, and then compensate accordingly. No tricks...

Happy shooting


Kaare
 

albert4321

Well-Known Member
Ken, thanks for bringing it up. Kaare is right on the money about the barrel extension phenomenon. When the 120mm focus to 1:1, it almost double its length.

For those that has done large format photography will aware of the barrel extension phenomenon. I have a formula some where for the barrel extension compensation with 4x5 camera, but I am not sure it will apply to this 120mm lens. I have to check if there is a table come with the lens.

It is more problematic if you do studio strobe light where you must use a flash meter. If you don't have the table handy, one of the easy way is to fire the pre-flash to see the different between 1:1 and infinity.

If you do some testing, you can find out the compensation factor quickly.

Bracket, Bracket & Bracket...

Al.
 

ksklo

Well-Known Member
Thanks guys. Unfortunately I had no prior experience with either medium or large format in the past. But this is a valuable lesson that I've learnt and I do appreciate all your comments.

I think for now the best solution is to use the TTL meter with a grey card. This way at least I can be sure of the exposure accuracy. And Albert, if you do find the table that you mentioned before, please kindly post it here so that other novices like me can benefit from it. By the way, I should have bracketed but I felt that the incidence light meter had been giving me perfect exposures in the past, and I just got lazy. Indeed a valuable lesson.

Thanks again everyone.

Ken
 
S

spluff

Ken,

Just one other thing, Gossens make a probe for their light-meters so that you can measure light in areas where it is difficult to stick the meter itself. This probe is ideal for macro photography.

You could ask Sekonic if they make one for their meters.

Cheers, Saras
 
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