Image of the day

Captured by
Troy Carpenter

2024 MAY 9 - Giant Sunspot AR3664

My Account

New to Astromart?

Register an account...

Need Help?

Posts Made By: Preston Engebretson

April 20, 2003 09:55 PM Forum: Telescope Making

A baffling question

Posted By Preston Engebretson

Hi Jeff,

"Telescope Optics by Rutten & van Venrooij starting page 227 discusses in about 10 pages the ideas behind baffle positions.

I've just finished an 80mm f 5.4 finderscope and I had 6 aluminum knife edge baffles in place. That with putting black felt on heavy card stock between the baffles made for fantastic contrast and no light reflections or glare.

Sorry, dont know of any website in general but the following link may have something

Hope that helps,


June 1, 2003 01:48 AM Forum: Equipment Talk

10" f/6 Zambuto vs. 16" f/5 Intermountain

Posted By Preston Engebretson


Even with a reputation...aperture rules...without calculting...your looking at at least 100% more light gathering...

If the Intermountain Optics are any good at all, the images will blow away any 10"....regardless of the maker...



ps You will see things with the 16 that you would only hope to see with the 10".....and then they would be faint fuzzy's!!!!!!!!

June 1, 2003 12:50 PM Forum: Home Observatories

balsa wood observatory model

Posted By Preston Engebretson


You might find some literature from a model shop or book on model building from someone like

I've been using balsa wood to work out design prototypes for the past 25 years, but it was basically trial and error during the learning process, but not too painfull...Much easier to take an exacto knife to a small bit of wood than a torch to a steel beam...

My latest project is a geodesic remote control dome built on the back garage roof, using stress skinned aluminum support walls somewhat like an airplane and a composite polystyrene/plywood/glass epoxy dome structure... the rolling shutter will be aluminum in 2 pieces.

I'll hopefully have everything finished by mid July and post pics.

Regards Preston

June 4, 2003 11:35 PM Forum: Telescope Making

Cookbook 245 VR4?

Posted By Preston Engebretson

Vr4 is a 78L12 chip....

Regards Preston

June 11, 2003 11:45 PM Forum: Telescope Making

Treating Aluminum ???

Posted By Preston Engebretson


Likely a heavy solvent like MEK ( methyl ethyl ketone) or Acetone will cut the grease after wiping all that is possible off of the tube...

Then tape of a small area of perhaps 10 cm square and do a test patch to see if the paint sticks well...

Then a phosphoric acid primer will be used to etch the aluminum prior to priming and painting...

Yes lots of steps, but a finish that will last a lifetime...



June 13, 2003 02:25 AM Forum: Telescope Making

Re: Shott/Schott? Glass

Posted By Preston Engebretson


They may, but I doubt that is thier fortay...

I'd look to others for mirror blanks...unless your are looking for a fused silica blank...for a secondary or small primary...



July 4, 2003 11:28 PM Forum: CCD Imaging and Processing/Solar System

Sunspot 375

Posted By Preston Engebretson

GY Fantastic images of the sunspots...Could you give us more details on the Picture and method of capture...Barlow, length of exposure and number of images stacked????

The detail is beyond belief!!!!!!!

Regards Preston

July 9, 2003 12:01 AM Forum: CCD Imaging and Processing/Solar System

mars image 8th July 2003

Posted By Preston Engebretson

Tan Wei...

Still a Very Nice Image...

Wish I had an 75 degree shot at Mars, rather than a max 42 I understand you comment about below 55 degrees!!!

Regards Preston...Keep the images coming...Thanks

July 16, 2003 12:27 AM Forum: CCD Imaging and Processing/Solar System

mars image 15th July 2003 1941UT

Posted By Preston Engebretson

Great Images!!!


WE've been under the clouds for the past 6 weeks....other
than 2 days at the full moon!!!!!

Hurricane has passed...

Let's get some images!!!!!!

We hope to produce images of this caliber close to late August....

Regards Preston in Houston Texas

August 10, 2003 10:24 PM Forum: Telescope Making

20" mirror blank

Posted By Preston Engebretson

Justin, You can find a variety of differing types of blanks at
Newport Glass...and they can pregenerate the curve, very handy
with a blank of that size. There are others, but I've not done business with them...