WO GTF-81 unboxing and first impressions

[mytola]

My 5 element flat field WO GTF-81 just arrived from Ian King, so I thought I'd post some initial impressions. No astro work yet unfortunately - Clouds and the Norwegian summer will be a limiting factor a couple of more weeks at least. I'm looking forward to test it properly as it's been subject to some controversy. The scope comes with a "QC passed" bumper sticker, however I've been recommended to check the collimation on the scope. Not sure how to do that without any stars though.

My experience with refractors is fairly limited. A long time ago I had a Celestron 60mm achromat, but I replaced it with a Celestar 8 after some years. So I don't really have much for comparisson. That said, I think the finish and mechanical quality of the GTF-81 seems very good. Compared to the pictures it actually feels a lot sturdier, and the 2.5" DDG R&P focuser is very smooth while having a solid feeling resistance. I haven't been able to detect any play at all, and It seems to me that focusing with this focuser will be a whole different world than focusing my C8s wobbly mirror. Although I have yet to attach anything very heavy. Focus can be locked by tightening a screw at the bottom of the focuser.

Included in the package was a small finder/guidescope with rings. The guidescope has a 1.25" eyepiece holder , and that's very convenient as I'll use it with my QHY5 to autoguide. The scope focuses by rotating the eyepiece holder, and focus can be locked by tightening a ring.

I've only looked at some lights on a distant hill as of yet, but they seemed nice and sharp. I'll have to take some pictures with my canon 40D when my photo adapter arrives. I've lokked inside the tube wih a flashlight, and it seems the included flattener sits just behind the focuser.

[Cjg]

Oh my, the new Williams refractor pictures at this late hour and before bed.

You must let us have a first light report as soon as you can please - that said clear skies in the UK are a little hard to find at the moment, so am sure we'll be patient

Chris

[mytola]

Trust me, I want to take it under some dark and clear skies as soon as possible. I must admit it's quite stupid to buy a new scope this time of year in here in Norway...should maybe have bought it with a solar filter...

[steppenwolf]

I'm really looking forward to your full review when you've had a chance to point it at the stars but thanks for this preliminary one.

[Marki]

Lovely looking piece of kit! Hope you get to try it under the stars soon!

Try the link below for advice on testing collimation (thanks to John for pointing me to this) - useful, but you'll want to star test it anyway

http://spacealberta.com/equipment/refractor/collimate.htm

[mytola]

Thanks for that! I actually have an eyepiece for collimating reflectors - I'll have to try it when I get home!

[DirkSteele]

I look forward to reading a first light report....Though given your location we might be waiting a while.

Clear skies,

Matthew

[mytola]

I just had a go to check the collimation of the scope with my Cheshire eypiece, and I don't know what I can conclude from it. I definitely did't see two black center dots, but sometimes it looked a little bit oval. Seemed to vary with the angle of my eyeglasses to the eyepiece hole though...

Took a picture through the front hole of the Cheshire with my macro lens:

Lots of variables in that picture like lens angle to the optical axis and lens properties, but maybe someone more experienced than me can get something out of it?

[Joost]

Looks like an impressive planetary nebula.........

I had a look at the satellite image of Europe, I'm guessing no clear skies any time soon in Norway.

[mytola]

Just what II was thinking

Might be some opening in the clouds this weekend, however it's not very dark. Maybe I can get some pics of the brightest stars...but better not jinx it

[Marki]

I just had a go to check the collimation of the scope with my Cheshire eypiece, and I don't know what I can conclude from it. I definitely did't see two black center dots, but sometimes it looked a little bit oval. Seemed to vary with the angle of my eyeglasses to the eyepiece hole though...

Took a picture through the front hole of the Cheshire with my macro lens:

Lots of variables in that picture like lens angle to the optical axis and lens properties, but maybe someone more experienced than me can get something out of it?

Allowing for a bit of leeway for if the camera is off angle to the tube, that looks pretty much ok to my uneducated eyes!

Hope the weather clears for you soon!

[mytola]

FInally I got to test the scope under some semi dark skies! It still not actually dark here due to the season, but there's a window in the middle of the night where some stars come out.

I started out with just looking at starfields in the Cygnus area, and even under these summer skies I really loved the wide field I got together with my ES 14mm 100deg eyepiece, and the focuser worked nicely with the heavy eyepiece. The field in this eyepiece should be about the same as in my aps-c camera, and I didn't notice any obvious curvature, the field seemed flat and nice. I haven't looked through a refractor for a very long time, but the stars are amazingly tiny rock steady points that snap nicely into focus in this scope and display beautiful color. I think the star views had a very nice feel compared to my C8 which often have all sorts of trouble with frequent collimation, wobbly focus and tube turbulence.

I'd planned a couple of messiers in the area, and I started with the open cluster m39 which displayed beautifully in the middle of the wide view. It seems this scope is very nice for big clusters like that. Next I slewed to m57 in Lyra as this has been one of my favorite objects with the C8. Here the aperture and focal length of the C8 wins, and under these skies and with the smaller aperture it was just barely visible in the gtf-81 with the 14mm ES and 9mm ortho. The Dumbell nebula m27 was also a somewhat bigger smudge. Darker skies needed for more contrast!

Overall, the visual experience I got with this scope was very nice given the circumstances, and star fields were very pleasing. Based on the visual experience I think this will be a very fine grab and go visual scope for me!

After the visual session, I thought I should do some star tests, and those made me somewhat uncertain, as I really don't know what to expect. The attached pictures are of Vega, in focus (just by focusing on the laptop screen, no mask), intrafocal and extrafocal. I compaared it to this collection of star tests for many refractors, and the color correction seems to be quite good as far as I can see, and on par with other triplets there. The white balance temp is the same as the camera suggested - 5800K.

What makes me a little bit worried is the last picture, where the center seems off. The other one seems ok except for an additional smaller ghost ring off the center. Don't know what that is..dust or collimation error? Also, I'm not sure why the out of focus images are so diferent...but maybe someone here knows? I'll have to take some additional images tonight if it's clear to verify these results I guess.

Finally, I've attached an image of the local daytime star around here taken with the scope

Clear skies,

[Interested]

I suppose it doesn't help when you buy a new scope with the advice "check the collimation"! I think the 'test' and decider will be in the first images you take with the scope? If they turn out good, with nice round stars then I think you can say the collimation is fine.

You can read my thread on the Esprit 100ED to get an idea of what bad collimation will do to your images (right-hand pic).

Regards,

[mytola]

You're right, I'll have to try to capture some star fields next time. Didn't have time to troubleshoot PHD last night.

It has to be said that the collimation was checked by Ian King before he sent it, and it was fine. So if it's off now it's likely to have happened in transit.

[mytola]

Had av really nice night yesterday, took this picture, it's just a stack of four 1min exposures and zooms at the corners. To me this looks really promising! Guiding graph wasn't perfect since I balanced the scope first without camera (need to learn to think of everything!). Getting really happy with this scope now!

Clear skies,

[Interested]

Hi Andreas,

The main pic certainly does look promising. Not sure about the corner zooms though - think you may have zoomed a bit too much as they are looking a bit 'pixellated'. I think DSLR's are probably worse for this than CCD's (bound to get someone dis-agreeing with me on that now!). I'm looking forward tp seeing your first proper images with scope. Having had no luck with the Esprit, and unable to obtain a GTF, I have now taken the plunge and ordered myself a Tak FSQ-85ED (So few manufacturers seem to be producing flatfield refractors!). I've not mentioned it to my better half - thought I would do what she does when she buys a new dress; leave it in the wardrobe until she notices and then say "what , new? Noooo, that's been in the wardrobe for ages!

Hope to see one of your GTF images soon.

Regards,

[mytola]

Pete,

They're 100% crops, so I guess there's a lot of noise there which combines with jpeg artifacts and maybe some default sharpening in the processing software that I forgot to zero down. All in all I think it's looks quite well corrected. At least it's not like your Esprit stars...

I would love a TAK also, but I need a new house more... I don't expect the GTF to perform as well as the top contenders, but it really fits my ambition and wallet, so if it can give decent flat views without any hassle I'm happy.

[Interested]

Andreas,

The GTF would have better fitted my wallet! I've been trying to get a flatfield refractor for some time now, what with the Esprit, and waiting for the GTF to arrive. I ordered one from Ian as well but he had issues with a couple of the batch so he sent them back & couldn't fill my order. I've not heard if Skywatcher have sorted the quality issues with the Esprit and given the rarity of the GT81, I doubt there will be many GTF's available again for a long while. At least with the Tak I won't be looking to upgrade again, and it should have good 2nd hand value - it's an investment.....honest . I think your GTF will prove to be a great purchase!!

Best wishes and happy imaging ,

[mytola]

Thanks for that, let the dark autumn nights come!

Looking forward to hearing your experiences with the TAK

Clear skies,

[Waylandscape]

Thanks for that.

I'm looking at this scope myself to use with my 5D so I'd be interested in any further thought or results you've had.

[kriss13]

I'am about to the the plunge

I wan to use it for visuals sometimes but I heard that the FF makes the focus difficult or even run out of back focus.

What to expect (difficulties, oddities, barllow problems etc.) for visual use versus a triplet with no FF built in?

(I will use it mainly for photo anyway)

thx