[ripit]

I haven't given this much thought myself but I have converted both Oly and Minolta lenses for PK use by simply accepting the longer flange distance as an extension ring effect and using them for close-ups only. Too lazy to shave the coupl'a mm's from the mount base. I'd note that transplanting cannibalizing lens mounts and caps to extension rings, bellows and short sections of PVC tubing makes 'hermaphrodite' adapters easy.

The rear element in many of the cheaper TC's you might scavenge for such a project are assembled with threaded sleeves. I DO know that a miss-adjusted or loose TC element can have quite an effect on focus but I've not attempted to intentionally re-calibrate a TC to compensate for a different registry distance -- you might try that.

H2

I have actually converted several lenses. It seems the construction of many teleconverters make it a very hard job compared to a lens, but I did get my hands on a vivitar minolta md teleconverter that has the whole lens assembly threaded in as a unit with a lock ring. It was simply a matter of loosening the lock ring, threading the lens assemble forward, and infinity focus was fixed. Actually I threaded it a lot forward and it focused way past infinity, but its still an incomplete project (I'll play with it and fine tune it).

[Greyser]

I would love to have a pentax 0.7x af converter but I'm on an ebay MF budget.

Correction: it is 1.7X

[ripit]

Correction: it is 1.7X

Yea thats what I meant, typo.

[Lowell Goudge]

I have actually converted several lenses. It seems the construction of many teleconverters make it a very hard job compared to a lens, but I did get my hands on a vivitar minolta md teleconverter that has the whole lens assembly threaded in as a unit with a lock ring. It was simply a matter of loosening the lock ring, threading the lens assemble forward, and infinity focus was fixed. Actually I threaded it a lot forward and it focused way past infinity, but its still an incomplete project (I'll play with it and fine tune it).

This w the kind I was thinking about when you mentioned the project. The single lens group lets you play with infinity focus properly but still this conversion is really all about finding worthwhile LONG lenses as I can't see using a 2x converter on a short FL

Having said that, if you have a few hundred, why not convert a Pentax 1.7x AF converter, the internal AF elements should make a conversion a snap.

[demp10]

or he pixel peeps and looks at the image mapped pixel to pixel

Don't you loose the big picture that way?

actually they need to be stuffed real birds, plastic lacks the fine detail of feathers necessary to really judge sharpness

That's true, but are the feather details a bit fuzzy to begin with?

[ripit]

This w the kind I was thinking about when you mentioned the project. The single lens group lets you play with infinity focus properly but still this conversion is really all about finding worthwhile LONG lenses as I can't see using a 2x converter on a short FL

Having said that, if you have a few hundred, why not convert a Pentax 1.7x AF converter, the internal AF elements should make a conversion a snap.

I don't really have a few hundred (though with the way I have been buying stuff to experiment with its getting expensive). Honestly, if I could get my hands on one of the pentax ones which I would love to have, I would probably use it as is instead of chopping it up. It would make a pretty good quality adapter though.

I am only using 2x lenses as they are cheap (been paying anywhere from 3-9$). This project is turning out to be a lot more complicated than just setting back the mount distance. I set back the canon one 6mm trying to get infinity focus (should have only been 3.5mm). It was later I found out about all the compatibility issues with teleconverters and the fact that some converters wont even work at all with some lenses. 1.4x or 1.5x converters might be a second stage after I work out some of the problems. I have a canon fd mount kiron 1.5x waiting but I'm not even going to touch it till I have perfected the process a little with easy to get, cheap 2x ones. Next complicated step is to figure out the relation of setting back the mount as opposed to moving the group forward and how it effects what lenses it works with. If that doesn't totally fry my brain and land me in the looney bin, then I'll keep experimenting on the cheap ones.

[Lowell Goudge]

or he pixel peeps and looks at the image mapped pixel to pixel actually they need to be stuffed real birds, plastic lacks the fine detail of feathers necessary to really judge sharpness

Don't you loose the big picture that way?



That's true, but are the feather details a bit fuzzy to begin with?

Re feathers, look at the chickadee on the first page of the thread, and remember 2 things, first this is a 300/4 and 1.7x AF TC and second as posted it was downsized to post at full 6MP resolution it is actually sharper

[RioRico]

Of course, a comon and fruitful use of cheap old PK-A-type TCs to to remove the glass and use them as macro tubes. They're usually cheaper than actual A-type tubes.

[pacerr]

as I can't see using a 2x converter on a short FL

As a general rule, and considering the TC as a telescopic accessory, I quite agree.

But I've found a TC useful on shorter FL lenses 1) when the kit is limited and 2) when used to solve a perspective or location problem as well.

As an example: With only the AF 28-75 in hand and the Pz-AF 1.4x in my pocket, I was faced with a situation where I wanted a narrow field-of-view both for framing a rural building without a messy background and to avoid including an extreme highlight that would have complicated metering and DR/EV compensation. Terrain prevented relocating to make the shot for many reasons -- trees, trespass, elevation, etc.

The TC provided a margin of flexibility that achieved the best possible results under the circumstances. My SP 80-200 would have been preferable but I didn't happen to have that beast along with me that morning.

That's the sort of utility I was referring to earlier when I mentioned the advantage of including AoV and perspective as well as telescopic effect in the TC equation.

@ Lowell: Lookin' forward to seeing more results from the 200-500.

H2

[Lowell Goudge]

@ Lowell: Lookin' forward to seeing more results from the 200-500.

H2

my intention is to take it down to lake Ontario during the may bird migration. Probably about the middle or just before mid may

I have already sorted out a Jobo jr gimbal head and mounting plate to balance the lens, and I have a better Beamer for my flash but we are drifting a little off topic.

[Marc Sabatella]

Yeah, but if you're usin' a TC it's probably because the financial alternative would have been an econ consumer zoom at f 8 or bloated ISO to get comparable IQ anyway -- or a serious crop from a lens shorter by 50%.

Well, maybe not f/8, but sure, the alternative other than cropping is indeed usually a longer but slower lens. If I am considering using a TC on, say, my M120/2.8, the alternative I compare it to is using my M200/4. If I consider usng a TC on, say, my M200/4, the alternative I compare it to is using my Tamron-made 70-300/4-5.6. But since it's pretty rare I'd actually have all this hardware with me, really, the choice I make is normally beween using the TC versus simply cropping.

And I've no doubt that some of the bad-mouthin' of TCs comes from folks that simply don't understand, and/or fail to compensate for, the significantly increased motion blur that accompanies longer focal length lenses.

There is a fair amount of confusion about this from from both sides, I'd say, and part of that comes from the fact that there are actually different ways of doing the comparison that makes sense depending on whether you are already shutter-speed limited or not, and also on whether you are comparing against a specific other lens or against cropping on the same lens.

In the case where light is so bright you just don't have to worry about shutter speed, then I would normally choose the single sharpest aperture available. That might mean f/8 for a the bare lens I am comparing against, but it might mean something else for the lens with TC.

In the case where light is limited so I'm trying to get the fastest shutter speed I reasonably can, I feel the most sensible comparisons are those that either hold shutter speed constant or else that give me the fastest shutter speed I can get for a given ISO - ie, shooting wide open. Both comparisons interest me.

I've done fairly thorough tests of this nature using my Kenko 1.5 TC on most of my lenses, comparing both to the same lens cropped, and to the next longer/slower lens in my lineup. I compared my 50/1.7+TC to my 70/2.4, my 70/2.4+TC to my 100/2.8, 100/2.8+TC to my 135/3.5, etc. Plus of course also each lens with TC t the same lens cropped.

As I've related, the only case where I ever found a win for this particular TC with these particular lenses was in the non-light-limited case for the M200/4. The sharpest aperture with TC was f/6.7 on the lens (which is a stop slower effectively), and the image at that aperture slightly beat the cropped image from the bare M200/4 at its best aperture, which was f/8. The TC image had a slower shutter speed, but got a sharper image. So, that one worked out OK for the TC. All other comparisons, however, were won handily by both the bare lens cropped and by the next longer/slower lens.

Motion blur from one source or another accounts for the great majority of my unsatisfactory long FL shots even though I'm careful to double-down on stability when usin' tele modes.

And something that I think people don't always take into account is that if you're going to crop an image, you need a faster shutter speed just as surely as you would if you had shot with a longer lens. That is, if you're going to crop an image from a 200mm lens to the same field of view as an image from a 300mm lens, you will need the same shutter on each to get the same average level of blur.

[ripit]

I'll go ahead and give my input of the whole crop vs teleconverter discussion since I just did a rather amateurish and half ass test. The teleconverter is a craig brand 2x that I paid 3$ shipped for on ebay (I bought it with the intention of using it for donor mounts). I just got it a day or two ago so I haven't tried it out. I was just curious how it was and thought of comparing. Lens was a sears 50mm 1.7 that I got kind of cheap. Camera is an ist-ds. I think the moral of the story here is going to be, what happens when you try to crop a lot on an old 6mp camera? I took pics with a tripod of the box for the idt-ds (had lots of text and graphics, some of the text is light grey that kind of fades out and becomes unreadable on really bad lenses, and it was just handy). I tried to compose so that the box almost filled the frame with the teleconverter on. I took pics at f1.7 and f5.6, with and without the teleconverter, without moving the tripod. I then viewed the pics on a 32" 720p sony tv. The pics with the lens only were viewed at 200% crop. The pics with the teleconverter were viewed at 100% crop. The pics with the lens were quite a bit clearer and sharper than the ones with the lens and the higher crop. The difference was more at f5.6.
Perhaps for those of us that are poor and have old 6mp cameras, glass is better than cropping, even with cheap glass. If anyone with an older camera would like to try it out, I would be interested in hearing the results as my test was a quick glance at what would happen.

Of course I hope to upgrade to a k-r or k-x soon so I may have change my perspective a bit.

[newarts]

Here's a test I just did with my equipment. About the only time I'd use a TC is when I can't get close enough to use my DA 55-300 cranked all the way out and wide open so that's what I tested. With my Kenko 1.5x on the 55-300 @ 300:5.8 autofocus still works even though the actual f-stop is about f:8.7. I see no big difference between the photos. (Cropping was the only processing done with Picasa on jpeg output)

[ripit]

I decided to do a little more quick testing. First thing I realized, is the kit lens is not as sharp as the sears lens, especially with a teleconverter on it. I assume because its a prime against a zoom. I decided to stick with the sears 50mm 1.7 for testing. I tested with an auto focus quantaray 2x teleconverter, a manual focus mc quantaray teleconverter, and a vivitar 2 teleconverter. Either the craig is better than I am giving it credit for, or the rest are crappier than I though (either possible, lol). Regardless, while they varied some, all beat the lens alone cropped down more at f1.7 and f5.6.

First off, does anyone disagree that this is probably because it is a 6mp camera with less resolution to play around with cropping, especially when displayed on a hdtv? Someone correct me if I am wrong, but going from a 100% crop to a 200% crop, is basically making a 6mp camera a 1.5mp camera? Second, does anyone think that this would translate to higher resolution cameras? For instance, would a 15mp k-7 do better with cropping compared to glass, than a 12mp k-x would?
Fyi, I did read the whole thread and do understand, that there are plenty of scenarios where the tc is better even if you loose a little quality. I also understand that quality of the glass is going to play a part in how well cropping compares to glass.

[newarts]

Has anyone posted an example or link to an example where a photo with tc is better than the cropped and enlarged photo taken with no tc but same camera & lens?