Altair Astro 8" f4 Imaging Newtonian

[Stephen]

This may be of interest

http://stargazerslounge.com/diy-astronomer/161854-mods-pressure-plate-altair-astro-focuser.html

[earth titan]

Tonights mission is to flock the OTA.

With all those lovely baffles, it seems a shame not to flock what I can. There is a large section in the middle, right under the focuser, that is crying out to be done so after tea, out came the tools and the Wilco's purchased flocking material.

You can see the area I mean:

[earth titan]

I'm not going down near the primary as there are no real surfaces to cover as it is so well baffled. So with everything stripped out (focuser, spider etc.) I started by applying patches of the flocking material inside. To do it in one go is a recipe for disaster as this stuff tries to curl on itself as much as it can.

[earth titan]

Finished all the way round now and while the focuser was out, I've popped a bit in there as well.

[blinky]

Good job, where and how much did the flocking cost?

Sent from my Scroll Excel using Tapatalk

[Stephen]

Good result How far up the focuser tube did you go?

Good job, where and how much did the flocking cost?

Sent from my Scroll Excel using Tapatalk

I'm not sure what Tom has used, but FLO have 45cm x 1m for £7

http://www.firstlightoptics.com/telescope-flocking-material/black-velour-telescope-flocking-material.html

[earth titan]

Just for aesthetics, if for nothing else, I also flocked between the baffles at the front. I suppose I could do it all the way down, but I'm not sure it would achieve much.

Looks cool though.

[earth titan]

And there we go.

All assembled, back together and ready to go.

Will need to collimate tomorrow night and fingers crossed we get some good weather soon.

[earth titan]

The flocking material was from Wilkos believe it or not. I bought all they had yesterday as I have an SCT and a Light Bridge to do as well.

£5 per roll I think. It is the same stuff FLO now stock. 1 roll was needed for the f4 scope.

See this thread for details:

http://stargazerslounge.com/diy-astronomer/164314-great-flocking-material-superb-results.html

How far up did I go? I went all the way between the sets of baffles and the front end.

[Deneb]

Tom, would you do me a favour, would you be kind enough to measure the optical tube from one end to the other & tell me the width of a baffle, using a ruler or using a digital caliper - from out to in please & also the size of the secondary.

BTW the flocking has made the newt look a lot better...

Nadeem.

[earth titan]

Managed to get 1st light this evening. Not a perfect night as there was a full moon to cope with. Mount handled the scope without a murmur and PHD tracked a treat.

Below is an image with some problems though. Strange shaped stars (I would almost suggest coma but I'm using a coma corrector).

This is the same for all images, independent of exposure time so not a tracking issue. Could it be a collimation issue? I have had both mirrors out already but collimation looks okay so any hints, gratefully received.

[earth titan]

And here is a stacked image.

I think the scope has a lot of potential (despite the odd shaped stars). This was a few hastily taken lights with no darks, flats or bias frames.

It was also a full moon, not more than a few inches from the target.

[blinky]

looks like pinched optics - check the collimation screws are not too tight . nice first light though.

[earth titan]

Thanks Blinky. After I made my post last night I checked the collimation and it wasn't bad enough to account for the distortion in the images.

I took the collimation screws (not the locking ones) out and added two more washers (they come with two on already). This gave more room for the locking screws which in my opinion, are too short and made collimation more difficult. With more washers collimation was much easier but I think it could do with some stronger springs as well. Might have to try to find some.

So how did 1st light go?

Well apart from the possibly pinched optics, a quick run down of the nights findings:

Won't focus without an extension piece

Should have expected it, as a dedicated imaging scope, but normal eyepieces won't come to focus. Camera is fine, but makes alignment interesting

Condensation

No evidence of condensation on the mirrors, despite the guide scope fogging up a treat. The outside of the OTA was running with moisture by the end of the night.

Camera shutter speeds

Vastly reduced from the ones I'm used to with an 80mm refractor. The M42 shots above were taken at about 20 seconds ISO 1600.

Tonight's job is to free the optics off. Might take the mirror clamps off as the silicon holds the mirror in place fine and this will reduce any distortion plus reduce flaring (thanks Blinky).

[blinky]

I bought spring from bobs knobs in USA - took a out 10 days to arrive and are much stronger.

I'm going to double check my centre spot and possibly remove and redo the silicone - this time with less! Any chance you have a picture of your silicone job?

[Catanonia]

Not another silicon pinching issue is it. Check the imaging discussion forum for two threads on this by blinks and myself. Try the method in my post with my 8 inches using a business card. I don't get triangles even at F2.8

[earth titan]

Having read the messages and posts from Catatonia and Blinky, I think too much silicon may be the problem. Apart it has come again then, to redo.

Previously I had siliconed the whole mirror in place, at almost every contact point but this time I have taken guidance from Stallarfanes website, which shows blobs of silicon used as resting pads not as an adhesive.

I have supported the mirror above the cell using equal packing to allow around 3mm clearance. The pads will then be 'sqidgy' due to their thickess. Once this has set, I shall check the ffit and gently shim the mirror to losely fit the side supports.

While the primary is out, I'm wondering about flocking the side of the primary. This would keep reflections down and be temporary so could come off if needed.

[blinky]

Tom,

I am about to nip outside and bring my mirror in to do the same - I like you, overdid the silicone!

[Stephen]

I've just finished mine, and I've taken guidance from what's been said in all the threads

I took the mirror out, then put three blobs about 3/4 inch long around the central ring (ensuring each blob was higher than the cork spacer the mirror sits on.)

The mirror has been laid back on, and gravity should do the rest now.

[Coco]

Am waiting for the result of the optics..

Also I would like to know the overall length of the OTA please

At that price I would mind a newt to play with..

.

[Stephen]

Coco : It's 32" long. (Hmm, that was from the site : I'm looking at it and thinking it's longer but can't find my tape measure!)

A picture is worth a thousand words It may need more, we shall see once it's all back together tomorrow (when the flocking arrives.)

[earth titan]

That looks fairly similar to my work, although mine are little further toward the edge. Just waiting for it to set now, so I can reassemble.

[Peter Drew]

Flocking the side of the primary mirror might insulate it and prolong the cooling down time.

[earth titan]

I've cleared out all the excessive amounts of silicon.

And here is the finish once it has been redone.

The 1st picture shows the rear of the cell. The paper is acting as a wedge to keep the pads as support pads and allow it to cure in place before I reassemble. This hopefully will provide movement and support. There are now only three pads.

The 2nd picture shows a close-up of the pads. I reckon they are about 2mm thick which should be plenty.

When it has dried, I will apply a little shim to the sides of the mirror to locate in the clamps. More about that in the morning.

[earth titan]

Flocking the side of the primary mirror might insulate it and prolong the cooling down time.

True. Can't think it would add too much cool down time, but will probably leave anyway.