Just borrowed an Optisan Star 70076

Sivakis · Post by **Sivakis** » Mon May 02, 2011 1:59 pm

As topic says, just borrowed my brothers Optisan Star 70076 reflector.

Cloudy nights so far so nothing much to see.

Anyway, this is how it looks like and what it comes with:

02 Barlows (2.0 and 1.5)

03 Eyepieces (SR4, H12, H20)

Some of you may have noticed that the slow-motion control rod seems to be askew. That's right, it seems to be broken.

Anyone knows where I may get a replacement for this?

Gary · Post by **Gary** » Mon May 02, 2011 2:08 pm

Btw, you can also try testing the optics on terrestrial objects during daytime or those red light bulbs at the top of HDB buildings at night.

Sivakis · Post by **Sivakis** » Mon May 02, 2011 2:17 pm

Yeah, I did some testing on objects opposite my block.

It's ok, all works but seems to be a bit "grainy" (like taking photos on ISO1600 or something).

Not sure if it's because of the eyepieces or the secondary/primary mirrors are dirty (it does look pretty smudgy looking down the barrel).

Gary · Post by **Gary** » Mon May 02, 2011 2:34 pm

Most probably the collimation is off. Get some better quality eyepieces and give them a try. Perhaps you can take a photo straight down the tube so we can see the condition of the mirror.

Sivakis · Post by **Sivakis** » Mon May 02, 2011 5:19 pm

Well, collimation is definitely slightly off, just from line of sight. Not possible to take a photo down the tube though, it just blocks off all light when my camera looks down the barrel.

Looks almost like fine layer of mould over the primary mirror. May look into taking it out for a wash.

Sivakis · Post by **Sivakis** » Wed Jun 01, 2011 10:15 am

Small update:

Still haven't had a chance to repair the broken rod.

Removed the primary mirror for a nice clean/wash. There were large patches of fungus growing all over. It's now nice and clean. Haven't collimated yet as the seeing is still pretty good.

Question though - now I want to plug my Canon EOS 500D into the reflector and am coming up short on options. Since the tube assembly is exposed to the air, if I use the standard

Camera => T-ring => T-adapter => telescope

option, my camera sensor is exposed to any dust particles floating in the tube assembly - something I definitely want to avoid.

I've heard of T-rings that come threaded and ready to connect to a filter but don't seem to have seen anything like that yet. Can anyone advise or direct me to where I may find this?

cloud_cover · Post by **cloud_cover** » Wed Jun 01, 2011 2:37 pm

Actually in whatever telescope you use, the sensor will always be exposed to dust in the telescope itself. I use my D700 with an open tube VMC200L as well and so far haven't had an issue with dust. Alternatively, if dust is an issue, you can simply blow the sensor with a puffer after each imaging session if you camera has a mirror lock up for cleaning mode

Additionally, I notice you're on an Alt-Az mount, which means you photography will be (very) short exposure so I don't think dust will be much of an issue unless you're in a VERY dirty enviornment.
regarding the adapters, is your focuser a 1.25" or 0.965" focuser? This will affect the size of adapter you need to use

I think its great you're restoring an old scope. despite all the hype about "new and shiny", I think old equipment can still do a very good job of opening up the heavens to us, especially since it can cut through some of the light pollution that has virtually switched off our night skies!
I agree with Gary though - getting 1 or two cheap generic plossls will be a good step up from the Huyguen's and Ramsden EPs you now have

Sivakis · Post by **Sivakis** » Wed Jun 01, 2011 4:48 pm

Thanks cloud_cover.

What I'm thinking of is to introduce a layer of glass (filter) between the T-ring and the T-adapter. Now I know that doing so will affect the viewing to a certain degree but call me paranoid

Yeah, you're right. I was so tempted to spring for the Orion StarBlast™ 4.5 EQ Reflector but trying this Optisan out first to see if I really want to get into it.

Maybe I'll look into getting new EPs also.

So many things to try... also wanna try making a barndoor for dslr shooting blah blah blah ......

shirox · Post by **shirox** » Wed Jun 01, 2011 5:02 pm

Hi Sivakis,

For EOS cameras, you may wanna consider these EOS clip on filters offered by astronomik.

They have many types of filters including owb, ha, oiii and more.
This will solves your fear of having dusts fall onto your cmos sensor.

orly_andico · Post by **orly_andico** » Wed Jun 01, 2011 5:22 pm

one other alternative is a coma corrector or field flattener.

both of these have lenses in them that will protect the sensor from the air. I pretty much leave my field flattener permanently on my old (modded) 300D.