What telescope is it?

[jeffwjz]

Hi,

I recently acquired a telescope from an auction. The telescope is said to be a Skywatcher 80mm apo triplet so I bid for it straight away. 

After receiving it, it has blue tube so should be one of those old skywatcher models, with a dial speed focuser. Looking at the wordings around the lens it does say that it's a 80mm f7 ED apo triplet. 

I tried to o search for some information and specs of this telescope but couldn't seem to find any useful information. 

Does anyone have any idea what model this is, and is it a good scope in general for astrophotography?

Thank you very much!

[GazOC]

I might be well off the mark here but are there any signs that the scope maybe made of parts from different instruments?

[John]

I agree with Gaz - tt's a hybrid scope made up from a Skywatcher tube, focuser and tube rings and an objective lens and lens cell from another manufactuer.

The dew shield looks too short so you will probably need to add an aftermarket dew shield such as an Astrozap or similar.

There were some very, very early Skywatcher ED100 triplets but just a handfull were made and they were F/10 so 1000mm focal length.

 

 

[John]

There were / are quite a lot of 80mm refractors that use an F/7 triplet objective so it could be from any of those.

[jeffwjz]

Thank you Gaz and John, the OTA does look like home made, as I noticed the dew shield rim is not actually cut straightly (doesn't look like the work from a factory). I'll try the scope out when the weather is better. But anyway I do feel it is a bargain for a £80 bid.

[John]

The objective and cell may be from a company called Intane Optics:

http://www.intaneoptics.com/lens-assembly

Assuming that the objective and cell are in good order, they alone are worth quite a lot more than you paid for the scope.

[GazOC]

Assuming things such as that the tube is cut to the correct length to achieve focus etc. then I think you've got a real bargain. 

I seem to remember those lens cells aren't cheap. One of reasons they didn't catch on much as upgrades was that there wasn't much/ any saving in just buying a  new ED80 instead of upgrading the lens cell in your achro 

[barkis]

Bit of blue overspray  on the focuser end, but no big deal.
A mix and match with a new colour job. ~
How it looks is less important than how it performs really.
That will reveal whether the buyer got a bargain.
I'm sure we all hope he did. 🙂
Ron.

[jeffwjz]

Thank you for your replies. I did notice that there is a little crack on the very edge of the objective lens - a bit disappointed. The rest looks all very good so far. I'll try it out hopefully this evening.

[Kev M]

8 minutes ago, jeffwjz said:

Thank you for your replies. I did notice that there is a little crack on the very edge of the objective lens - a bit disappointed. The rest looks all very good so far. I'll try it out hopefully this evening.

I doubt you'd notice to be honest.....imagine the impact of a secondary mirror and 4 supports in front of your main lens ( ok mirror ), yours will still be sharper than any reflector.

The impact of minor lens damage and the effect on the final picture is much overexaggerated.

[John]

The damage probably won't affect the image but I'd be interested in how it got there and whether an impact (if that was the cause) has affected the alignment of the 3 elements in the objective. If they get a bit out of kilter they can be somewhat tricky to realign.

Re-sale value would be affected by the damage of course, even if it does not have an effect on performance.

 

[GazOC]

I bought a 150mm f5 refractor off FLO years ago that had a small chip in its objective lens, as far as I can tell the chip has zero effect on the views the scope gives.

Steve from FLO kindly sold the scope off very cheaply because of the damage and I've always felt I got a bit of a bargain 

Edited June 4, 2019 by GazOC

[barkis]

I guess it's natural for those who buy these, may  I say exotic instruments to pay close attention to performance. Understandably so considering the price that comes with them. I think the imaging  fraternity are probably more likely to scrutinise performance than those guys who are primarily observing devotees. I don't wish to seem unkind to either of them, it's just an impression I have, and an impression that I may have completely wrong.

Don't misunderstand, I can appreciate the nice feeling that owning one of these superbly crafted instruments will give it's owner, but is it possible that the desire for perfection can make the smallest perceived anomaly seem huge ?   I would die for a 152mm Apo. but I dream on.😀

Ron.

[John]

46 minutes ago, barkis said:

I guess it's natural for those who buy these, may  I say exotic instruments to pay close attention to performance. Understandably so considering the price that comes with them. I think the imaging  fraternity are probably more likely to scrutinise performance than those guys who are primarily observing devotees. I don't wish to seem unkind to either of them, it's just an impression I have, and an impression that I may have completely wrong.

Don't misunderstand, I can appreciate the nice feeling that owning one of these superbly crafted instruments will give it's owner, but is it possible that the desire for perfection can make the smallest perceived anomaly seem huge ?   I would die for a 152mm Apo. but I dream on.😀

Ron.

If the damage is restricted to a small chip to the glass I agree that the impact on performance, even for visual folks like me, will probably be invisible Ron.

If the lens elements have become decentred due to a knock then the difference will be noticable and tricky to correct. I'm cautious when it comes to triplets

 

 

 

 

[barkis]

9 hours ago, John said:

If the damage is restricted to a small chip to the glass I agree that the impact on performance, even for visual folks like me, will probably be invisible Ron.

If the lens elements have become decentred due to a knock then the difference will be noticable and tricky to correct. I'm cautious when it comes to triplets

 

 

 

 

Of course John,  the how and the why is important, and other possible consequences of 
that damage would need to be examined. The elements in the cell housings cannot possibly be held in vice like grips,
be they doublet or triplet, so any physical shock could produce misalignment for sure.

 

[jeffwjz]

I tested the scope for visual last night by looking at Vega. I've noticed that the tube may be a bit short for the objective lens, as I need to roll the focuser back a lot to reach focus. Clouds rolled in quickly so I was unable to try with the ccd camera. Also there is no finder bracket on the scope which is a bit inconvenient. 

17 minutes ago, barkis said:

be they doublet or triplet, so any physical shock could produce misalignment for sure.

I don't think it's possible to know how the lens was damaged in the first place since it's an auction item. But is there a way to check the alignment of optics? I did try to use laser on the eyepiece holder and the exit beam comes out on centre of the lens. 

Thanks. 

[John]

A star test on a star such as Polaris will reveal any obvious issues with the scope optics. It should be done at high power (150x - 200x) and with the scope cooled down.

The image below shows what a good star test looks like using an artificial star. A real star presents a similar image. The diffraction rings either side of focus should be circular and concentric around the central airy disk. If they are skewed in some way and / or not circular then that shows collimation or alignment issues with the scope optical system. Ideally you should do this test without a diagonal in place to eliminate the diagonal itself causing any issues.

At sharp focus the star should be a tiny circular dot perhaps surrounded by one faint diffraction ring.

 

[jeffwjz]

Finally got a chance to try out this unbranded refractor. I took on NGC6888 with Altair Astro field flattener and Ha filter, with 5x 15min subs. Looks good enough to me. The field flattener may not be adjusted to its best spacing though. 

[jeffwjz]

Also, when I was testing the focus of this scope using a bahtinov mask, I noticed that - after I reach focus using red filter and then switch to a blue filter, the star pattern became slightly out of focus. To me it suggests that all lights are not focused on the exact point although the objective lens claims to be a "triplet ed". Is this normal for all apos? I would expect apos should be able to focus all lights at a focal point, as this is how they're designed to be. 

[GazOC]

I've never owned a triplet but I think that's normal. The lenses don't focus the different wavelenghts of light at *exactly* the same point 

[jeffwjz]

10 hours ago, GazOC said:

I've never owned a triplet but I think that's normal. The lenses don't focus the different wavelenghts of light at *exactly* the same point 

I see. I not an experience refractor user, so I guess in the case of astrophotography, it is necessary, or recommended, to re-adjust focus for each channel for RGB imaging? 

[DaveS]

Yes, even with a triplet. Blue especially can be out of focus compared to the other colours, as it's at the limit of correction, the dreaded "blue bloat" (Sound like a horrible disease).