I'm looking to buy a 10" dob (maybe the Mead lightbridge). Can someone explain the "Four-Reticle Red Dot Viewfinder" and how it works. I'm familiar with a typical finder scope, as at the moment I have a small 4" reflector.
All pictures of the scope I'v looked at do not show any finder.
What do you look through ?
Having trouble deciding between solid tube or collapsible.
Any info/advice would be appreciated.
Thanks
Richard
Last edited by richardda1st; 10-05-2009 at 12:11 AM.
The "Four-Reticle Red Dot Viewfinders" (pic attached) are very easy to use, and I now prefer them over conventional finders. But I have found the cheaper single-dot versions to be pretty useless.
They project a small red dot (or cross-hairs etc) onto a slightly tinted viewing window. You just nudge the scope until the dot coincides with the star through the viewing window.
The easiest part is that you still have your peripheral vision to see plenty of sky (rather than peering down a narrow finder), so initial target selection and rough alignment is very easy.
I find the single red dot annoyingly bright, and the single dot tends to blind your night vision.
There are two ways to improve this - an array of four dots so you can see the target centred in the dots, or alternatively make the red dot blink so it is on for about 0.2s each second. The latter is an easy mod to the cheap red-dot finders, using a 555 timer and a soldering iron.
Er, or can't you just select one of the other reticules?
Personally, I like this particular finder, better than the others, but still a pain when looking at zenith. They need a flip mirror...
Cheers,
Brian.
Quote:
Originally Posted by Wavytone
There are two ways to improve this - an array of four dots so you can see the target centred in the dots, or alternatively make the red dot blink so it is on for about 0.2s each second.
I have a 200mm Dob that came with a right angle finderscope that I found difficult to know exactly where I was aiming my scope in the sky.
I purchased a Four - Reticle Red Dot Viewfinder and find that it is a great asset when used in combination with my right angle finderscope.
You will find that you need to have it set to the lowest illumination setting.
I find that the circle / cross setting the best to use, as the Dot tends to blot out stars.
I have a 200mm Dob that came with a right angle finderscope that I found difficult to know exactly where I was aiming my scope in the sky.
I purchased a Four - Reticle Red Dot Viewfinder and find that it is a great asset when used in combination with my right angle finderscope.
You will find that you need to have it set to the lowest illumination setting.
I find that the circle / cross setting the best to use, as the Dot tends to blot out stars.
cheers, Ric.
Richard, a Telrad is a similar type of unit, except for a single dot, they have 3 concentric rings which can be adjusted in luminance. A lot of people swear by a Telrad. I'm sure they have been discussed on IIS in much detail.
I've been leaning toward a 12" collapsable Dob but still undersure which is the best to get for my viewing. I m going to join ASWA tommorrow, get some more practical advice there. I feel this the best move forward for anyone seriously looking at a new scope. I bought an off the shelf cheapy and made a serious mistake there.
Quote:
Is there any lose to image quality in an open section tube compared to one piece tube.
I have seen some fabric around some larger DOB so i suppose that could be done with the smaller ones.
Hi Richard, welcome aboard. (Sorry, I missed your first post. I thought I was answering Jeff.) The Telrad and the multi-reticule finder are what are known as unit powered finders, i.e. they do not magnify. The first was the venerable Telrad, which is good but large. It was designed by Steve Kufeld, basically an adaptation a typical "head's up display" or "bomb-sight display" used by the US air force. Imagine a gun sight tube, or the red rectangles projected onto the windscreens of fighter plane's that fighter pilots use to line up enemy planes with their guns. (Same deal with those simulation computer games.)
Thanks to all regarding the red dot viewfinder, suppose I should try one out first. Have to find the time to get into Melbourne and check out York and Bintel.
As to my other queries, I will start a new request for advice, a new thread I think. Obviously I'm new to internet forums.
I feel well qualified to answer your question re. choice of dob, having gone from a 10" Bintel (GSO) dob (rigid tube) to a 16" Lightbridge (yes I got aperture hungry).
When talking a 10" I would go for the rigid tube without a doubt, providing you can transport the scope (my 10" tube took up the front passenger seat in my Ford sedan, with the base on the back seat). Of course, I've assumed here you do need to transport. If in doubt go to an astro society field night and check out the size of the 10" dobs.
A 10" tube is not that heavy and I found the collimation pretty good most of the time. I don't know your level of experience but a truss tube needs collimating every time you set up ( I recommend a lazer collimator). Sometimes I even have to reposition the secondary (something easiest done in the daylight). There is no need for a cooling fan on this size, I just allowed about an hour (sometimes running my aircon in the car to cool it down before arriving at my observing site - something sometimes not popular with the odd passenger in the back seat!)
re. finders, I've had a telrad for years - love it.
Advanced Four-Reticle Red Dot Viewfinder
