Televue 2.5X Powermate vs Sigma 1.4X and 2X Teleconverter (1 Viewer)

Yvan Bedard · Feb 13, 2009

Hi all,

I thought you might find this comparison interesting and could give me some explanations.

Tested on Televue 85 with Nikon D200

Result = Sigma TCs win !

Explanations and discussion are here:
http://photo4fun.zenfolio.com/p231550804

I suggest that you download the original photographs in order to really view the big difference.

Since I already had the Sigma TCs, I returned the Powermate to the vendor.

Comments are welcome,

Yvan

Paul Corfield · Feb 13, 2009

That's really bad, almost too bad that maybe it was faulty. Only reason I say is because I guy in my long thread on the link here posted a photo taken with a 2.5X Powermate and it wasn't anywhere near as bad as this. Scroll up to just over halfway and there is a post number #468 by a user called Gleeman. The photo he posted is of a dove and there's an uncropped version and a 100% cropped version. The photo doesn't exhibit the edge softness that yours does although I wasn't impressed with it purely because of the cost of the Powermate. I've seen other photos taken with Powermates that weren't all that good to justify the cost which has put me off getting one. As you noted, teleconverters can be really good performers.

Paul.

Ultra Lite · Feb 14, 2009

Yvan Bedard said:
I thought you might find this comparison interesting and could give me some explanations.

That's far too poor a performance to justify the conclusion that the powermate is a dog. Something else is going on besides a real difference in quality. I don't know what.

For instance following taken with a 25 buck 2x GSO barlow through an APO triplet. Full frame. Surely a properly set up powermate could do at least as well.

Yvan Bedard · Feb 14, 2009

Paul Corfield said:
The photo doesn't exhibit the edge softness that yours does

I've seen other photos taken with Powermates that weren't all that good to justify the cost which has put me off getting one. As you noted, teleconverters can be really good performers.

Paul.

I fully agree with you, and the Canon camera used has the same sensor size as mine !

One difference between my photo and the one on the post you mentioned is that I didn't have the T-ring especially made for the Powermate as the one mentioned in this thread. I had to use the Powermate at full lenght + normal adapter with T-ring, and consequently the distance between my sensor and the Powermate lens was about 4 inches longer... this could explain part of the problem...

Nevertheless, the Sigma 2X TC still gave better results while being easier to install and being shorter (thus less prone to vibrations).

I'm not sure it is worth trying the 5X Powermate (too dark) as I think I can get better results with normal eyepiece projection.

Regards,

Yvan

Yvan Bedard · Feb 14, 2009

Ultra Lite said:
That's far too poor a performance to justify the conclusion that the powermate is a dog. Something else is going on besides a real difference in quality. I don't know what.

For instance following taken with a 25 buck 2x GSO barlow through an APO triplet. Full frame. Surely a properly set up powermate could do at least as well.

This was my primary conclusion: it was sooo bad that I couldn't believe it. Something must be wrong: bad sample (never heard of bad samples from Televue) or bad installation.

On one hand, I used the only method possible for my TV85 and my Nikon D200. However, as replied in my previous post, I didn't have the T-ring adapter for the Powermate... Could it be it ?

Unfortunately, there is no email address to contact Televue...

Regards,

Yvan

JGobeil · Feb 14, 2009

These specialized barlows seem to be designed for astro work. On the TV site, they never mention using Powermates for short distances like birding; they seem to be designed for astro work. On the birding section of the TV site, they don't suggest it as an option either.

Could it be that the Powermate design includes a field flattener ? This could explain the edge distortion when used for short distance photography.

Anyway, given the price of those Powermates, I don't see why we would use them for birding, considering the good results we are having with TCs and barlows.

Yvan Bedard · Feb 14, 2009

JGobeil said:
These specialized barlows seem to be designed for astro work. On the TV site, they never mention using Powermates for short distances like birding; they seem to be designed for astro work. On the birding section of the TV site, they don't suggest it as an option either.

Could it be that the Powermate design includes a field flattener ? This could explain the edge distortion when used for short distance photography.

Anyway, given the price of those Powermates, I don't see why we would use them for birding, considering the good results we are having with TCs and barlows.

Good point Jules !

FernandoBatista · Feb 16, 2009

Your results are similar to what I had with my 2x powermate, I also returned it. Got a set of TCs later and couldn't be happier.

Don't know if I also had a bad one, I think maybe they're not really suited for this use.

spyaround · Feb 19, 2009

Hi gents.

Here's the adapter ring for the Powermates: http://www.optcorp.com/product.aspx?pid=105-182-220-224-2813

That webpage states "The magnification power will vary, dependent on the spacing between the top surface of the Powermate optics and the imaging surface of the chip or film negative. When using the 2.5x Televue Power Mate, magnification decreases linearly from 2.5x at a 1mm spacing to 2.2x at a 100mm spacing. With the 5x Powermate, the magnification increases linearly from 5x at 1mm to 7.75x at 100mm".

Televue's webpage at http://www.televue.com/engine/page.asp?ID=42#MagChart shows a graph http://www.televue.com/images/eyepieces/PowermatePowerIncrease.gif that supports the above statement:

The pink line is the 2.5x Powermate and it reduces magnification as you increase the spacing, and I guess your test evidence, Yvan, suggests image quality deteriorates as well as magnification. But I suspect that had you used the 2x, 4x, or 5x you might have gotten significantly better results. Or...the results for your 2.5x Powermate might likely have been more favorable had you removed that 3" spacer and connected your NIKON D200 directly or much closer to the Powermate.

Paul Corfield · Feb 19, 2009

On the link with the graph, Televue say "Telecentric operation (field rays leave parallel to optical axis, unlike Barlow lenses which diverge rays)." If this was the case then magnification shouldn't change no matter what the distance between the Powermate and camera sensor. With a telecentric lens the image should in theory remain the same size so Televue contradict themselves by then putting up a graph that shows the image does change size when the distance of Powermate to sensor changes. I can see now that having the 2.5X version as close as possible to the ccd would be the best option for this model.

Siebert Optics make some nice barlows, including telecentrics. One day I will get around to sending off for some.

Paul.

Yvan Bedard · Feb 21, 2009

spyaround said:
...the results for your 2.5x Powermate might likely have been more favorable had you removed that 3" spacer and connected your NIKON D200 directly or much closer to the Powermate.

Hi,

It is right that enlargement changes when the distance between the lens and the sensor changes. When I made my experiment, the 3" extender was between the Powermate and the the primary lens, not between the Powermate and the Camera. I needed to insert this 3" extender to have the image properly focused (it was impossible without it).

Regards,

Televue 2.5X Powermate vs Sigma 1.4X and 2X Teleconverter (1 Viewer)

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