I've been looking at ways to get to a 400mm focal length affordably and with decent IQ. While saving up for a big boy telephoto, I happened to realize that I had 2 TC-16As (one modified to work and autofocus on my D7100, and one unmodified) that could be stacked to get me that additional reach. My longest primes are currently a manual AI'd 200 f/4 QC and a factory AI'd 180 f/2.8 PC, so it wasn't long before they went on my stacked TCs to see if it would work at all. Below are my observations and a link to sample images. Would appreciate if others could look at the samples and share any other observations, or any thoughts on how the results could be improved.
Look forward to your comments and reactions.
- Link to sample images (all SOOC jpegs, handheld with AI'd 180 f/2.8 PC and two stacked TC-16As, except where noted): https://www.flickr.com/gp/89411942@N04/y8998Y
- Using the 200 f/4 QC on the stacked TCs resulted in too much AF hunting indoors, even wide open, and what photos I got didn't look great, so I didn't bother testing it further.
- The 180 f/2.8 PC, on the other hand, seemed to work pretty admirably (with certain limitations) with the stacked TCs. I was able to get decent shots at lower ISOs and shutter speeds than I would have expected with 2TCs and the long focal length (460mm f/7). All of the test shots linked above, and observations below, are with this lens and stacked TCs.
- Given I was stacking TCs, I expected images to be horrendous. However, I was surprised to get surprisingly detailed shots for subjects within 25 feet. Given the light loss due to the TCs, use of a flash helped considerably, although it often introduced CA in the catchlights. Use bounce flash if possible for reflective objects.
- Shots at wide apertures near the min focusing distance were often soft, but I expect that is due to the thin DOF at those distances which makes focus vulnerable to slight movements of the camera to or away from the subject.
- Beyond 75 feet to infinity, the detail was not great, as you can see from the moon shots or the BIF shot. To begin with, if the second TC-16A (the one that sits on top of the TC-16A that is attached to the camera) does not have its element extended all the way out, the setup doesn't even focus at infinity. Once I ensured that, I was able to focus at infinity, but the shots were terrible as you can see. Any tips to fix that will be appreciated. If it is even possible, I will be blown away, as it will give me the option to use this rig for BIF and distant birds, although I suspect a single TC with cropping might give superior results.
Look forward to your comments and reactions.
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