Testing a Tele Convertor

Hi,
How does one test the image quality(Sharpness) of a Tele Converter and its effect on a lenses performance.

Take a picture of a target with the standard lens, then fron the same position take one with the tele convertor, crop and enlarge the standard image to match the tele one and compare.

or

Move away from the target with the tele converter to match the image size on the sensor.

Greg


SMC Pentax AF TC Adapter 1.7x
Vivitar MC 2x PK-A/R-PK Tele Converter
Soligor 2x C/D 7 AF Pz/AF Tele Converter with SMD contacts
Tokina RMC Doubler P/K

Either way you'll see the degradation of the image. Generally only the very best teleconverters are useful and these cost as much as a marque lens.

This is very true. I have tried several converters and eventually ended up buying the "brand name units". I recently acquired the Pentax 1.7AF for use with my M series 200 and 300 lenses. I then tried it with the 50-135 and it works VERY very well, AF speed is awesome!

Other units are the Sigma EX 1.4 on my 70-200 Sigma EX Mk1 and a Nikon 1.7x on a Nikor 70-200 AFS VR.

Third party converters that are good are Kenko but as John says, they are costly. A good converter is worth the cost.

Regards

Thanks,

I have too many tele converters and want to compare them and make a final choice excluding the Pentax 1.7 which I'll keep.

Vivitar MC 2x PK-A/R-PK Tele Converter
Soligor 2x C/D 7 AF Pz/AF Tele Converter with SMD contacts and screw drive.
Tokina RMC Doubler P/K

Greg

You don't say which camera/lens combinations you may be using with the converters, or if you need auto focus. However it might be worth remembering that screw drive AF will not work if the combination is set up for SDM. So the Soligor may be useful.

Hi,

The cameras are K200D, K1000, ME Super and the lenses are
SMC Takumar M42 f4.0 300 mm
SMC Pentax M f5.6 400 mm
SMC Pentax K f4.5 500 mm
SMC Pentax K f8.0 1000 mm

The Pentax 1.7AF does sometimes manage to focus but I do not depend on it to do so.
The auto functions of the converter are not important to me as all my lenses are manual focus, I'm trying to establish a testing method to see which converter will give the best image for those occasions when I need to get the last possible bit of reach from a lens or whether I must settle for a cropped image.

I'm also trying to avoid buying a Pentax Rear Converter A 1.4x-L

Greg

More reach than a 1000mm lens....

Indeed and that on digital APS-C camera
Do you've a nice neighbour that you try to photography in the shower, never thought the houses would be so far from each other.

So the smaller the sensor, the larger the magnification?

I'll try my Pentax 110 with an adapter behind a 650 mirror then.

Regards

Stefan> How I wish that were true,

Kris< I very seldom have the 1000mm lens with me, it's a bit awkward to use in the car.

This picture is what started my query. It was taken from the car with a Sigma 50-500mm resting on a sandbag. F8 at 1/250 in RAW format

When I got home expecting to see some beautiful crisp shots I was very disappointed and even after some heavy PP they are still not up to my expectations.

Greg

Try taking a picture at 500mm and then at 250mm with the Teleconvertor.

The images should be near identical and easier to compare than having to crop and enlarge.

Hopefully, I will see a few secretaries when I arrive in 10 days - complete with DA*300, M400-600 and A2xS Teleconvertor. I have used the 400-600 and A2x together and also an A70-210 plus A2xS with good results.

I used one of those combinations to capture a distant eagle in flight. The eagle was just around 192x136 pixels but still possible to see the individual wing tip feathers as a set of fingers. It may be out of focus slightly, but at that distance and speed!

Eagle:

[IMG]http://i2.photobucket.com/albums/y31/Polchraine/PentaxForum/IMGP0861_crop.jpg[/IMG]

Te EXIF data just says A lens so it could be either ... and it was 5 years ago! And close to Knysna.

The original was saved as PEF, then converted to JPG using the Pentax software and the Highest Quality setting to give a 2.5MB file. Since then I have just cropped it today.

Thks, I'll do a test as you suggest. I hope you enjoy your trip and get lots of photo opportunities.

Greg

stupid question Greg, but just to be sure you are aware you need to do a bit of manual pre-focusing with the lens before the AFA can get it properly focussed ?

I've only used my AFA with A-series lenses, so I'm intrgued to know how you handle the exposure for K, M series?

Thanks, I learnt about pre-focusing the hard way, about 20 years ago I ordered a tele-converter from Hong Kong to use with my SFXn body. When it arrived they had supplied a 1.7AF converter and I could never understand why it did not focus and sold it in disgust for peanuts, "I know stupid"

I use manual mode and the Green button to set exposure. K200D.

Greg