DOI 3X teleconverter (1 Viewer)

I didn't know DOI made a 3X teleconverter until I saw two of them on ebay this week. On the auction I bid on at the weekend I won it for just £4.99 and shall post some photos when it arrives.

Paul.

This one arrived in the post this morning. Weather is terrible today with quite gusty winds which means very little bird life around. Here's a direct comparison with the Kenko Pro 3X and the target was a moss covered rooftop around 30m away so there's plenty of little details in there from a decent distance. Open up both photos and flick back and forth. The images are straight off the camera and just resized. No cropping, no level adjustment and no sharpening.

I'd say the DOI 3X is excellent and about the only difference to the Kenko 3X is that the Kenko has slightly better contrast which in turn gives the colours more saturation. The DOI 3X is only a little bigger than the average 2X and it's a lot smaller than the Kenko 3X and build quality of the DOI is excellent. Most common mount is probably going to be Pentax so if you have a Pentax or Samsung dslr and want a 3X TC then this is one worth seeking out. There's one on ebay at the moment but it's a good deal dearer than the £5 I paid for this one.

Paul.

Couple of images from long range at 85m. First is uncropped and second is a crop. These were taken in very strong winds so it's not ideal conditions for this much magnification. Quality is pretty much the same as with the Kenko 3X though which is impressive.

Paul.

Thanks for your tests. How do you compare a decent barlow (2x) (not sure what you have at the moment) to these ? of course not really being comparable, these being 3x, but i think I recall you saying that a barlow lets in more light and to prefer over a converter. But I may have misinterpreted. Thanks for your comments.

cango said:

Thanks for your tests. How do you compare a decent barlow (2x) (not sure what you have at the moment) to these ? of course not really being comparable, these being 3x, but i think I recall you saying that a barlow lets in more light and to prefer over a converter. But I may have misinterpreted. Thanks for your comments.

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I'll do a test tomorrow, weather permitting, and see how they compare. My 2" GSO ED barlow is my best one and I can put a macro tube between the camera and barlow to bring it up to 3X magnification. The main issue with barlows is they need a much longer extension tube in the back of the scope to allow you to reach focus. The 3X teleconverter only needs 50mm to allow focus down to around 7m. The barlow would need at least 80mm to allow the same. Barlows also suffer a lot from internal reflections ruining the contrast of the photo. I think this is mainly down to them having too much shiny paint around the barlow housing. These are all things to consider where as a teleconverter works straight away.

Paul.

I think that DOI 3x is so close to the IQ of the expensive Kenko, that it'd be silly to buy the Kenko now you've proved the point

Good work

Musoman said:

I think that DOI 3x is so close to the IQ of the expensive Kenko, that it'd be silly to buy the Kenko now you've proved the point

Good work

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The DOI 3X is such a rare one though and probably even rarer in Nikon mount and not available in Canon EOS mount that only Pentax/Samsung DSLR owners can really make use of it. Only other option is to buy a Max DSLR or T-mount in Pentax bayonet and use a Pentax adapter ring for the camera. That's what I did for my Canon 450D as all my telescope stuff and lenses were Pentax mount from when I had a Samsung DSLR. But yes, it's as good as the Kenko and certainly worth buying as a cheaper alternative. If I had a load of lenses that I could use a 3X with then I'd probably get the Kenko as it has all the electrical connections.

Paul.

cango said:

Thanks for your tests. How do you compare a decent barlow (2x) (not sure what you have at the moment) to these ? of course not really being comparable, these being 3x, but i think I recall you saying that a barlow lets in more light and to prefer over a converter. But I may have misinterpreted. Thanks for your comments.

Click to expand...

Did a quick comparison with the 2X GSO 2" ED barlow. I had a 90mm macro tube between the camera and barlow to boost the magnification. It's still not getting to 3X so you would probably need something like a 120mm macro tube which is getting a bit long really.

These are all from 70m approximate range, measured on google maps. The levels haven't been adjusted and they are all shot at the same speed. All were hand held but mirror lock up would have produced sharper results. There's very little difference between the DOI and Kenko versions. The Kenko gives at a guess about 0.1X more magnification and the colours are a little more saturated. The Kenko has more contrast but could maybe have done with one drop in shutter speed. The barlow still works well though even with all that extension.

Also posted an image of the two TC's side by side.

Paul.

Paul, that's really interesting about the Pentax route. Could save a fortune compared to the kenko/nikon brands

Would the following work together in the way you suggest?

DOI

Adapter

T-mount

Thanks

Marco

PS - I think with all the testing, research and advising you do consultancy fees will be in order soon or at least commision :t:

Yes, that combination would work but personally I'd probably avoid it. The thing I would be wary of is that the Pentax to Nikon adapter has a small lens in it and that could be the weak link depending on its quality, especially as all those adapters tend to come from Hong Kong etc. I've not heard good reports about image quality from them.

DOI teleconverters do come up occasionally on ebay for Nikon mount so I'd wait for one of them.

All the adapters for all the other mounts seem to need the small lens in them. The purpose of that lens is to allow you to reach infinity focus with whatever camera lens you mount. I doubt the lens is needed for the scope to reach focus so it could be removed as a last resort.

I'm hoping to get one of the Jessops ones soon just to try out. If it's no good I'll just sell it on again as they tend to hold their price well enough.

Paul.

Many thanks for the comparison done. The barlow shot looked ok, but the converter a bit better, I think. I understand the need for "perfecting" the barlow contrast - perhaps via flocking it, thus getting rid of unwanted reflections. One other thing I believe have read, is putting the barlow lens as close as possible to the camera (you did a special mounting). I have on order a 2x barlow (celestron ultima. Had a gso barlow before, but accidentally scratch it while fiddling around with it...thought I'd give it one more go) - and I'm not after a 3x - 2x is ok, but putting it so close to the camera may give me less than 2x, is it so? well, if it's so, no problem, as long as it gives me good picture detail. Long reach is ok, but I prefer to work within the closest focus I can get, up to 30m, perhaps more on bigger birds. (though I more often chase after the smaller ones)

to sum it up: did you see an increase in picture quality having the barlow lens close to the film plane, than further away (if all flocked properly) and how much magnification do one loose?(or not)

Your opinion will be VERY appreciated, so thanks again.

I think the barlow one would have looked fine if I'd used mirror lock up and shutter release cable. My own GSO is covered in little nicks and scratches as I'm always trying out different ways of mounting it. How much magnification you get varies from barlow to barlow. The GSO gives around 1.5X when it's mounted as close to the camera as possible.

The Celestron Ultima will give you quite a lot of magnification even with it close to the camera. I had one in the past and found it gave around 2.5X. It's not an easy one to get close to the camera because you don't really want to be taking out the glass elements. I think they are air spaced so you need to leave them in the chrome barrel. I mounted the chrome barrel in some plastic tube that was a tight fit in my scope adapter. I found it hard to baffle and stray light was an issue but if I had another one I think I could do it a lot easier with what I have learnt since. Easiest way I have found to baffle a barlow is get a regular metal washer with a similar outer diameter to the barlow and use one with the smallest hole you can without getting any vignetting. Just stick it on the front of the barlow with some Blu-Tac or something similar and that should do the job. With the GSO barlow I cover at least 50% of the glass to get the contrast really high.

I've got an Antares 3 element Apochromatic 1.5X barlow at the moment and it has awful internal reflections. It comes up fine when I stick a metal washer on the front tough. Quality is as good as the Kenko 1.4X TC and because it's an apo design there is zero CA.

Paul.