My one’s longer than your one..... 😉

[Stu]

Grant very kindly sent me a ScopeTech STL80A-L 80mm F12.5 Classical Refractor in order to compare it with the F15 version which I still have on loan.

Tonight looks like it will be clear at least for a while (though there seems to be a band of cloud heading this way). I’ve just popped them both on my Ercole mount on the Gitzo tripod which handles them very easily. I’m using a Tak prism and a Baader Zeiss prism to try to keep things even, and will try to match magnifications using BGOs of varying focal lengths, or my Nag Zooms for very high power stuff.

I’ll add more to this thread later, assuming I get some viewing in, and then ongoing as I get more time with them.

Price is not really a deciding factor between them (the F15 is £434 vs £419 for the F12.5), so it’s really about optical performance, field of view and practicality due to the scope length.

The F15 is 1200mm focal length vs 1000mm for the F12.5. The best true match I will get is with a 6 and 5mm BGO giving x200 in both, perhaps of some use for tight doubles.

Anyway, let’s see how this goes. Watch this space.

[Roy Challen]

They both look nice, but I can't help thinking that there isn't enough difference in focal length between to be worth it. Still interested in hearing your opinion though! I like the little sights they have, would be nice to know if they're any good.

Edited March 30, 2021 by Roy Challen

[johninderby]

Will be interested in the comparison.

The little sights are not much use really. I suppose if you didn’t have a finder fitted they would be better than nothing. 

 

[tuckstar]

9 minutes ago, johninderby said:

Will be interested in the comparison.

The little sights are not much use really. I suppose if you didn’t have a finder fitted they would be better than nothing. 

 

I just have those on my telementor. Really good for just pointing at bright stuff, and no need to faf lining up a finder. Useless for dso!

[John]

Interesting comparison.

I hope you have clearer skies than I have here Stu

Both should show very little to no CA according to the Conrady and Sidgwick standards. It will be interesting to see if either scope has any advantage in other areas due to the focal ratio difference.

F/12.5 is going to be a bit easier on mounts.

It's good that traditional instruments of this type are still available to buy new. They practically died out a few years back.

[johninderby]

Old style scopes but with the advantage of the latest lens coatings. 👍🏻

[JamesF]

28 minutes ago, johninderby said:

The little sights are not much use really. I suppose if you didn’t have a finder fitted they would be better than nothing.

I thought they were attachment points for a handle.

James

[johninderby]

1 minute ago, JamesF said:

I thought they were attachment points for a handle.

James

Could be used to attach a carry strap I suppose. 😁

[JeremyS]

I’m all 👂👂  Stu. Will be very interesting 

[Alkaid]

Following with interest...

[Stu]

Oooooh, the pressure

A couple of comments:

I found the sights actually quite useful for lining up on Sirius before getting the finders aligned. So, useful on bright stars and the Moon for instance but less so for faint stuff.

I just had to remove the Baader clamp I had fitted to the F15 because even with the Tak Prism, which must have a short light path, the BGOs would only just reach focus right at the stop. I put the original fitting back on (which is not great because of the single set screw) and I now have a bit to play with. BGOs do focus quite a long way in compared with other eyepieces so others may not have this problem.

Using the 6mm and 5mm in the F15 and F12 respectively giving x200 in both I was looking at Sirius early on. Not much doing here I must say as it was flashing around quite a lot in the poorer seeing down low.

I’ve just spent quite a while looking at a few doubles to try to see a difference. So far, the only difference I can discern is that the F12 seems to show a slightly brighter first diffraction ring than the F15. I take from this that the F15 is keeping more in the airy disk and there is an almost imperceptible difference in terms of disk brightness in favour of the F15. I have switched prisms to rule that out and the effect is the same. It is subtle but definitely noticeable. I have looked at Castor and Algieba, and each looked fabulous through both scopes. I tried the tiny double in the 37 cluster and it was resolved in both, so I need to find a tighter, more challenging target! Unfortunately 32 Orionis is low now and I could only get the vaguest hint of a second star, not close to a split.

Any suggestions for tonight?

I’ll give Izar a go when it gets a bit higher which should be easy in both. Not sure I will hang in there until the Moon gets high enough as tomorrow is a ‘school day’...

That’s all for now.

[John]

Interesting stuff Stu

A brighter 1st diffraction ring is the main difference between my Vixen ED102SS F/6.5 and Tak FC100-DL F/9, interestingly.

Don't know if you have a view of Auriga but Theta Aurigae is a nice uneven brightness double. Not all that tight though.

Zeta Herculis later on ?

The closer pair of Tegmine will be beyond 80mm I think but you might see a "notched pair".

Edit: Zeta Herc is a bit unfair on 80mm's really I guess

 

Edited March 30, 2021 by John

[John]

Iota Cassiopeia ?

 

[Stu]

Thanks for those @John 👍

Iota Cass was in a bad place in the sky, and I agree, Zeta Herc would be a bit mean for an 80mm 😉.

I gave the other two a go though. Theta Aurigae was interesting. The secondary actually seemed a little easier to spot in the F12.5 as the brighter first diffraction rings seems to clean up anything outside of it. The secondary was outside this ring, so quite easy to spot. In the F15, which the airy disk was perhaps a little brighter, there was more ‘noise’ in terms of broken diffraction rings further out, albeit fainter, and that made the secondary a little harder to spot. Interesting effect.

Tegmine was as you suggested, easy enough split for the wider pair, and a notch for the tight pair. It may have been a fraction more defined in the F15, but really nothing of any significance. Actually finding Tegmine in the first place was quite a challenge as the brighter stars in Cancer were barely visible to the naked eye. I popped a 24mm Panoptic into the F12.5 and found M44 which looked very good, pinpoint stars to the edge, the target filling the field of view. I then had to starhop across to Tegmine using SkySafari.

Izar was another example of that brighter diffraction ring causing a different effect between the scopes. In the F15 the secondary was clear and separated, with a faint, and mostly interrupted first diffraction ring. With the F12.5, the secondary was clear still, but also sitting on a very well defined diffraction ring, very much like a gemstone set in a ring! Still quite obvious and defined as an airy disk, in fact it was very beautiful to look at.

Finally a quick look at the Moon, and I focussed on the crater Petavius which looked essentially identical in either scope. I did think the might be one small peak bit visible in the F12.5, but a tiny tweak on the focuser then showed it up so this was a draw.

So, so far nothing that is visible in the F15 that is not visible in the F12.5, just that brighter diffraction ring in the F12.5 which is separating them optically at the moment. More to follow when I get the chance.

Just for interest, here is a picture of the two scopes side by side, with my Telementor for comparison. 840mm vs 1000mm vs 1200mm.

Thanks,

Stu

[John]

Very interesting Stu - I look forward to more on these scopes in due course

Petty much a waste of time trying to observe here this evening. Got a few glimpses of stars in small holes in the otherwise rather thick clouds.

Glad you had better luck

[johninderby]

I found the Vixen HR 3.4mm worked really well on the moon with the F15. Of course that was with good seeing.

They could do with making the f/15 tube a bit shorter to allow for more infocus. I suppose as the scope was designed for the Japanese market where they tend to observe without a diagonal  that wasn’t a consideration. 

There is a solution.............. 🪚🪚🪚

Edited March 31, 2021 by johninderby

[Sunshine]

You weren't kidding, yours is much longer than mine! that must make a great planetary scope with a Km focal length!

[Stu]

6 hours ago, johninderby said:

I found the Vixen HR 3.4mm worked really well on the moon with the F15. Of course that was with good seeing.

They could do with making the f/15 tube a bit shorter to allow for more infocus. I suppose as the scope was designed for the Japanese market where they tend to observe without a diagonal  that wasn’t a consideration. 

There is a solution.............. 🪚🪚🪚

I’ll give the Nag zooms a run out when the seeing is better. In theory I should be able to match the mags at about x300 with 4mm and trying to find 3.3mm ish on the other....

Yes, agreed, you can definitely tell they have been designed around the straight through market. Whilst I don’t particularly like the standard rear fitting, it did just give me enough infocus to work with vs the Baader replacement clamp. A short optical path prism also helps, and probably choosing eyepieces which need less inwards focus, unlike the BGOs. I was pleased I got them to work though as they are very sharp obviously.

Both scopes are very lightweight. I could pick the whole rig up with one hand quite easily to reposition it to a different part of the garden when I wanted to see the Moon as it rose.

If anyone has any other target suggestions, do post them up and I will give them a go. I may also have a stab at taking some star test images to post up for comparison, although from what I can see they are pretty much text book. Some CA visible out of focus, and perhaps the slightest hint of being less defined inside focus than outside but pretty marginal. Optically both are excellent.

[F15Rules]

Beautiful scopes to look at, Stu, just simple and elegant lines, great colours ( you can't beat white IMO😉), and both just shout " Doubles"!

So far, it sounds as though there is little to choose between them based on your notes..I've always liked the large Airy disks that these long fracs put up...it's interesting how you're finding that closer doubles can be perhaps slightly more or less easy to split in either scope, depending on the location and brightness of the companion star vs the first diffraction ring and it's brightness?..

I remember that the two best double splitting long fracs I owned it looked through were either F12.5 or F15. The former was a wonderful Pentax J80,  (80mm F12.5) looking extremely similar to the Scopetech 12.5mm you are using, and the second was of course "Andromeda", the superb D&G USA 128mm F15, which is now in the care of Steve (Saganite), and which looks at first sight like a missile launcher at over 6' long.

The stellar images put up by both of these were simply superb on good nights ( and still great on not so good nights!).

Please keep the observations coming Stu.. I'm basking in nostalgia here!😊👍.

Dave

PS: here's a link to the thread and some pics of the Pentax J80 when I bought it..can't believe it was 11 years ago!!😱😁

 

Edited March 31, 2021 by F15Rules
Additional photo and text infoo

[JeremyS]

Something missing from that frac, Dave @F15Rules?

 

[F15Rules]

4 hours ago, JeremyS said:

Something missing from that frac, Dave @F15Rules?

 

er..Dusty Bin? Bicycle? Tube Clamp? Red Ink? DFCs (Droopy Flexible Controls)?..

Nope...sorry, Jeremy, I've got to handle it to you, you've got me this time

Dave

[johninderby]

Can’t think of anything myself. 😁

Edited March 31, 2021 by johninderby

[Stu]

You guys, what are you like? 🤪🤪

Actually, when carrying the scopes back to the house last night, I naturally just held them by the dovetail which works very well as a handle, no mods needed really.

[johninderby]

On a slightly different tack wish the Orion focus wheels were still available. I had a pair of the brass focus wheels so I used those. They do make focusing a bit better. Wonder if it would be possible to obtain a pair of SW aluminium focus konbs as supplied on some of their focusers? 🤔

[Chris]

Listening with interest : ) and I'm sorry I just couldn't resist...