6" f/10 refractor build.

[AndyH]

Very interesting indeed.

Always wondered about whether baffles, matt black paint or flocking of some sort, would be best. I have heard of the Televue flocking solution also.

The paint I use for stuff is, 'International Matt Black'. I just painted the inside of my homemade dewshield on my newly aquired Carton 60mm achro and it's worked a treat(details in the classic & vintage link in sig, if anyones interested.)

Out of interest, how did you 'stick' the baffles in position?

Cheers,

Andy.

[Doc]

Going back to the light cone diagram, do you simply bisect at 90° the light cone and then measure the truncted light cone dimension to give you the size hole in the middle of the baffle.

So this way you could in theory place aa many baffles in as you want. Slide them onto your three pronged dowel system making sure you have a few millimeters clearence before your baffles hit the tube.

Then secure the dowels top and bottom of the tube.

Would this work?

[Jim!]

Thanks for the writeup Argo, looks to be a lovely well made scope. I'm a bit partial to shiney ally.

Looking forward to first light report - I'm within a gnats buttock of buying a short focal 5", I'll be using you as a guinea pig :)

[Towa]

Stunning looking scope. First light will be a real treat.

For Matt black paint, I use plasti-Kote Flat Black B2 Fast dry Enamel.

Once painted, I put my tubes into a long thin box with an electric blower heater on one end, I then bake the tubes.

As with all paints, it's best to try it out on an off-cut first, just in case you get a bad reaction with the paints used.

[argonaut]

Andy,

Thanks for the tips on the paint. I will look into this.

Mick,

Yes,I did measure the baffles off the light cone drawing.Knife edge baffles are the best,but you must keep checking for vignetting with focuser. I made the baffles quite a tight fit in the OTA. I can now remove the baffle unit if needed.

You can in theory place as many as you want,but I needed enough space on the baffle plate for the 3x8mm holes for the rods to hold the baffles in place. I wouldn't like to glue each baffle to the OTA.

Jim,

Go ahead and build. The satisfaction gets the old ticker pounding a bit. There is lots of help available on the internet.

Towa,

Thank you for your tip also on the paint. I am going to look into this. Some ATMers in the States have used Krylon. It's still not easy using spray cans on longish OTA's

[argonaut]

Jim,

Just thought I would add that I had first light last Saturday night

[Jim!]

I promise to keep up and pay attention

In all honesty, I'm torn between making a nice widefield refractor with the iStar optics or starting to grind my own mirrors.

[Towa]

It's still not easy using spray cans on longish OTA's

That's the problem. I think in the 60s, Kenko had the same problem with their f/16 scopes. There answer to the problem seems to have been to paint the very ends and leave the middle of the tube plus baffles un-painted.

Towa at least managed to get their f/15 tubes painted, but going by the 14 inch paint-run inside mine, they tended to over cook it.

[argonaut]

I was thinking about anodising at one stage. There is a process available for Matt Black. I suspect this would be expensive.

[argonaut]

MIRRORS! What are they ?

If you don't like CA,then don't go short tube.

[Jim!]

Home anodizing

Been thinking about trying it for some time now. There are better websites out there explaining the process.

My GCSE kids do electrolysis without acid afterall, with propper safety equipment and acid handling it should be ok.

I was thinking about anodising at one stage. There is a process available for Matt Black. I suspect this would be expensive.

[argonaut]

Thanks for the link.I'll have a read.

[SpookyKatt]

Jim,

Just thought I would add that I had first light last Saturday night

..............So how was it Argonaut ??????

Kathleen

[argonaut]

Hi Kathleen,

Well..............It certainly didn't perform like an ED doublet,even with the f/10 focal length. I didn't expect it to. I had chatted with Ales from Istar Optical before purchasing,so I did know it was good,but not THAT good

The set up in the backyard took around 5 minutes with the help of my long suffering better half.

The temperature difference was from 25°C to -1°C. The NELM was around mag 4. Some high haze and a little bit of cloud.

I let the scope cool down for just 15 minutes (I know,I know,I couldn't wait any longer) I used a 32mm eyepiece(47x) and focused on Polaris. I picked out the companion very easily. Polaris looked pretty White to me,so the CA was not evident at this stage. I put in an 8mm eyepiece(190x) and immediately saw swirling tube currants. It had only been 15 minutes

30 minutes went by and I tried Polaris again and noticed the tube currants diminishing. I put in a 4mm (BGO)eyepiece(381x)The Airy disc was circular,both inside and ouside of focus and illuminated equally.

45 minutes had passed and the tube currants had disappeared completely.The Airy disc also looked cleaner.My next observation was Mars with the 32mm.It was washed out and CA was now rearing it's ugly head. Mars was still low though and this would not have helped.A little Green at the top with Mauve at the bottom. I tried with the 8mm next and managed to see some shading on the disc.

90 minutes(I was getting cold:)) and the Moon had risen enough for a look. I observed using the 32mm,it was certainly bright. The CA was Green all around the disc. It didn't seem to reduce the image so bad though. What I did notice is that when I switched from my Brandons to my UWAN's the CA was now Mauve with no Green in sight.

I did try a few more favourites out,M45,NGC457,Castor,Mizar/Alcor.

When I brought the tube back indoors it was of course covered with a satin coat of moisture. It was interesting to watch the polshed tube appear has it warmed up from the thinnest part to the heavier parts.It did take around 1 1/2 hours to warm up again.

I am going to try a Baader semi-apo filter to see if it will improve the CA.

The Giro 3 mount was excellent and worked a treat. With the tube being 58" long I might attach a small weight system to the OTA. I could change eyepieces without losing the object but with a small weight system it may be easier. Something to think about.

Apologies for going on a bit.I'm not known for good reports

[AndyH]

Nowt wrong with that report !!

Keep us updated.

Cheers,

Andy.

[Doc]

Not knowing your past astronomy endeavours how you compare this against other ED scopes?

In laymans terms was it a success, harsh words but apart from the thrill of making it does it deliver from ready made scopes?

[argonaut]

Hi Mick,

I don't mind harsh words at all. I'm here to learn also. I would like to hear other peoples comments on what I've done. I've got a thick skin:)

My last three scopes have been a TV85,two of those,and a Equinox 120ED.

There is no comparison to an achro. The Equinox with it's fpl53 and Schott secondary was an excellent scope and I would recommend the Equinox 80 or 120 to anyone. The TV85,which I have owned two of over the last 15 years is one of the best scopes I've ever used.I can only assume the that TV also uses fpl53.

It's been along time since I owned an achro and I must say I was taken aback a little by the CA. I do intend to work on the problem trying filters and possibly a new corrector Ales is working on.

I've only had first light and I need to do more observing. I think I'm on the right track with the lens,and I would buy from Ales again. What would be interesting would be a 6" f/10 ED. I know another ATMer in the UK is working on the f/12 version of this achro. I am eager to see the first light on that.

Looking at it in the overall sense I'm pleased so far with just one observation.

[dweller25]

I found a light yellow filter reduced CA just as much as a (much more expensive) semi apo or minus violet filter. It does give a yellow tint but I soon got used to it.

[AndyH]

I found a light yellow filter reduced CA just as much as a (much more expensive) semi apo or minus violet filter. It does give a yellow tint but I soon got used to it.

I'd second giving a yellow filter a go, before splashing out on a more expensive devoted CA killer. Can remember, years ago giving this a go, to decent results.

That chromatic devise, that Istar has in development, is very interesting. Will be interesting to see how it works out.

Cheers,

Andy.

[argonaut]

Yes,thanks Dweller and Andy. I've tried the filters in achro's I owned years ago. It's the cast that puts me off. Although saying that,all achro's are not made the same and I will give it a go with this objective.

I think it might be the big binos tonight which are f/5.3

I can see a little cloud building up already

[philj]

Fascinating thread and report Argonaut. I am really impressed with your scope, my hats off to you for tackling a project like this.

I am in the process of upgrading an older F15 scope and have used a similar method to you with the ray tracing for the baffles, only I did mine on CAD. Similarly I intended to fit maybe 5 baffles but have now resigned myself to three due to complexities.

The yellow filter is a good idea, a few years ago I tried a minus violet on a shorter fl achro and found it too agressive.

Keep the reports coming

Philj

[Doc]

I wonder what the Istar 152mm F7.5 APO lens is like? A llittle expensive at $3250 though.

[AndyH]

If I remember rightly, the Williams Optics CA reducer(can't remember the name), was one of the better ones in tests. Good at ridding false colour and not introducing much of it's own.

Andy.

[argonaut]

PhilJ

I have never used CAD.I've often thought of trying out one of the free programmes just to see what it was like. It would be interesting to start a thread on the refurbish of your scope. I'm Rubbish at explaining things and I've had a go

[argonaut]

I wonder what the Istar 152mm F7.5 APO lens is like? A llittle expensive at $3250 though.

I had a look at this Doc,but the price was out of my league. We are all looking for the Golden Fleece.Paying achro prices for ED performance. Well, with correctors being worked on it may help to attain this,fingers crossed

We could start another debate:evil6:

FPL53 doublet versus FPL51 triplet.