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Bushnell telescope


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I just acquired a Bushnell model 78-3650, 700mm focal and 76mm objective lens. Could you tell me if this thing is worth a Rubbish or not? I'm excited to have a telescope and also hope it's decent enough to do some sky watching.

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Just about any scope is worth having. Most of us would have sneered at the optics that Galileo used and yours are probably better than that, the mount has a reputation of being a bit wobbly and it will show a bit of false colour but shouldn't be too bad. you should get great views of the moon. jupiter and the galileon moons saturn and its rings and a few of brighter dso's. It has a couple of issues ie It has a very narrow field of view and a small apparture. But if you want a scope to start you off, get you hooked. and leave you wanting more it will do. I started with something similar. Actually I didn't I couldn't afford anything like that as a kid but a mate had one and although it wasnt a premium scope it did its job. I am still interested 50 years later I have actually just found a pic of the scope and have to revise my critique. First its not a achromat as i first though its a small reflector so it will not have any false colour. The spherical mirror means it will not be super sharp at high mag but if its properly collimated it will not be too bad in fact its a fair bit better than a cheap achromat in some ways but you will need to make sure the mount is tightened, the scope should be especially nice on the moon. I hope you enjoy it

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Isn't the 76/700 usualy a mirror telescope / newtonian?

If so it's a nice starter telescope, though not worth too much. They sell used for 15-30€, sometimes more. The next step up would be a 114-130mm telescope, usualy sells for 40-80€.

Build a dobsonian mount and it will be much more stable, http://ringohr.de/tmp5/sky125900_2.jpg (right side, costs about 4€ to build)

Also consider:

2 new eyepieces. 8-15€ (shipped) Plössl eyepieces or even better UWA (nice ultra wide angle view) 32-40€ shipped.

Not a must, but make observing so much more fun and tracking and finding easier.

With 76mm you can get nice views of Saturn and Jupiter at around 140x when they are up further again.

9.5mm Plössl for about 10€ and a better 2x Barlow for 16€ plus a overview eyepiece to give you the maximum field on a 1.25" focuser, something like a 30mm Plössl for 15€... Then you'll have

30mm=23x=3mm exit pupil (should be between 0.5 and 7)

barlow, 46x

9.5mm = 74x, barlowed 147x, 0.5mm exit pupil

So with magnifications like this, the telescope is ideal for viewing planets, brighter deepsky objects such as the dumbbell and ring nebula, star clusters like in hercules, Andromeda and Orion nebula, and many other things! I'm sure you'll have lots of fun.

But especially for deepsky, 5", better 6 or 8" will show much more details, and are really an amazing step up.

Of course the eyepieces alone would cost you 40€, nothing wrong to observe with the included stuff, I did not mean to discourage you! ;-) Just if you want to get the maximum out of it, they are great... And once you switched to better eyepieces, you don't want to miss them.

Have fun with your telescope!

Make sure to print some free star charts, download stellarium (telescope view ctrl+o, alt+o) and cartes du ceil, and perhaps astro tools (android app, but even red mode screens will ruin your night vision)

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Thanks for all the information guys! I have one lens that it came with. A RK 20mm, which doesn't tell me anything yet?

Also you talk about magnification, how do you change that?

Sorry if the question are really novice, just trying to get a good handle.

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Something else i forgot to ask about is the aperture. The end cap has about a 1.5" aperture, but if I take the end cap off it opens up to about 4 3/8", which when looking at an object about 200' away really brightens the imagine. Anything wrong with doing this?

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Sorry if this all was too fast, it's hard to tell what level of experience new members have :-)

The telescope"s focal length divided by the eyepiece's focal length equals the magnification.

700 divided by 20mm would equal 35.

For another magnification, you would need another eyepice or a barlow lens that doubles it.

As with barlows and also zoom eyepieces, usualy the image in a fixed focal length eyepiece is best. Similar to camera zoom lenses VS fixed focal lengrh lens.

Rk stands for reversed Kellner, and is a rather old eyepiece design, but not the worst.

Other then magnification there are certain other factors that will play a big role in eyepiece selection.

One of them is the apparent field of view. Looking through some eyepieces is like looking through a narrow pipe, while on some modern eyepiece designs you hardly notice the border anymore at all.

Hyugens have a 30 degree apparent dield of view, Kellner about 40.

Plössl 50, and that's where viewing starts to get fun.

Erfle, UWA eyepieces usualy have 60 to 70 degree afov, and sort of a "wow"-spacewalk-experience. While even these are available for under 50€, there are eyepiece designs for 100 to 1000€ with 80, 100 and even 120 degree afov now...

I know, lot's of information, perhaps a starter guide is a better source of information and better organized, too. But aesthetic aspects aside, a wide angle eyepice makes it easier to find and tracj objects, especially at high magnifications. Due to earth's rotation, planets will move out of view on a narrow afov within a minute or so.

Another importaint aspect is chromatic abberattion (when light of different color does not meet in the same focal point, giving you blue and yellow seams around bright objects, but this is usualy well fixed in modern eyepiece designs).

As telescope get larger, the focal length does not. Else you would need a ladder and larger eyepieces to achieve lower, overview magnifications.

Focal length devided by apperture equals the focal ratio.

Yours, beeing 700 / 76, is somewhat around 9.

Almost all eyepieces work well with f/9.

On larger telescopes, such as 250/1200 f/4.7 for example, Plössl, Erfle and such won't show a sharp image across the whole field.

Some get bothered by it under f/8, some accept it even at f/5.

In the beginning this won't concern you much, but as you upgrade, and perhaps plan for a larger telescope, it's neccessary to consider when you enter the world of aperture feever and the crazy world of eyepiece selection.

For now I'd recomend that you pick up either a cheap used eyepiece or some of the suggested above, as planets will start to get interesting above 100x ;-)

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Could you take an image of your telescope? :-)

Well some telescope lids have a smaller opening in case you want to observe bright objects (moon), but it limits your resolution as well.

Also, just a side note, for observing the sun a suitable filter is required. Sometimes old telescopes have one to screw onto the eyepiece, which is dangerous.

A sun filter belongs infront of the telescope, and needs to seal tightly. Else instant blindness and/or bursting eyepieces can be the result...

Moon filter, often delivered, help to preserve your night vision, and boosts contrast, but the moon's not harmful.

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you change the magnifiction by changing the eyepiece. magnification equals focal length of scope (700) divided by eyepice focal length(20mm) equals 35x. as to the end cap I dont suppose you could show a picture could you as I am not sure what you are driving at. The end cap should be somewhere around the 76mm mark as that's the size of your objective the 11/2 inch one is I am guessing your eyepiece which are usualy 11/4" a picture says a thousand words so if you could upload a snap. edit I see the gentleman above has already answered much better than I have

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Great, sorry for all my typos (a bit tired and on mY mobile phone).

Try setting up a telescope in Stellarium (ctrl+o, alt+o) and the following:

Telescope, 76mm aperture, 700 focal length

And one with 200 1200mm

Stellarium won't simulate brightness, resolution and such, it allways shows the perfect view in full color. BUT it is great to simulate eyepieces and field of views.

Now set up a 20mm eyepiece with 40 degree afov

and one with 70 degree afov.

Now tpe into search & view the andromeda galaxy for example. And the Plejads.

You will see that in your narrow view eyepiece, the object won't fit into the view, even though the magnification is identical.

Now add a 4mm eyepiece with 30 degree and one with 70 degree afov.

Klick outside the eyepiece view to loose the tracking, and you'll see how fast the planet will leave the view, and how hard it is to find it again using the arrow keys after a while

:-)

IF that's too much of a hassle try http://www.sternfreunde-muenster.de/orechner.php

I know it's german but almost self-explanatory.

Set up your telescope, and a 20mm eyepiece.

In the drop down menu, choose Kellner and Erfle, switch to other objects on the bottom.

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Yep, that's identical to the white telescope on mY images earlier.

If you have a saw, nails or screws, a few boards and some laminate flooring scraps, you can build a awesome stable dobsonian mount that will be much more stable.

When I first started with this telescope, finding Saturn and keeping it in the view of field was a bit of a hassle. So it's definitely worth considering :-)

http://blog.pixelgiraffe.com/wp-content/uploads/2013/06/minidob_3d_sketch.jpg

http://ringohr.de/tmp5/76dob1b_1.jpg

http://ringohr.de/tmp5/simplesimplemount.jpg

Due to moving atm I don't have pictures of the more recent, simpler version in action.

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Something else i forgot to ask about is the aperture. The end cap has about a 1.5" aperture, but if I take the end cap off it opens up to about 4 3/8", which when looking at an object about 200' away really brightens the imagine. Anything wrong with doing this?

Nope!

Take both caps off the front so you have a big open hole.

The little cap is to enable you to stop down the 'scope (to reduce brightness, you've discovered the opposite!) when looking at the moon, I've never understood why you'd want to do that myself, but there you go!

You can also take the small cap off when allowing the 'scope to cool down before viewing, if you're worried about the elements or other bits and bobs getting in.

Cheers

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Yep, that's identical to the white telescope on mY images earlier.

If you have a saw, nails or screws, a few boards and some laminate flooring scraps, you can build a awesome stable dobsonian mount that will be much more stable.

When I first started with this telescope, finding Saturn and keeping it in the view of field was a bit of a hassle. So it's definitely worth considering :-)

http://blog.pixelgir...b_3d_sketch.jpg

http://ringohr.de/tmp5/76dob1b_1.jpg

http://ringohr.de/tm...simplemount.jpg

Due to moving atm I don't have pictures of the more recent, simpler version in action.

I like the hand made DOB base. Have you got a link to the topic or video by any chance?

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I have Not finished a tutorial yet, as it's still a prototype. The aim was to make it as simple and cheap as possible. If you can get the Hardware Store to cut the pieces for you, all you will need to use nails or screws ;-) Half an hour build Time, Tops.

Wood planks, 24x48mm, 0,30€/Meter

Drill head screws, 3x45, 2000 cost about 8€ ;-)

Or nail gun that takes long 31mm nails.

Laminate flooring, scrap pieces, Free at the Hardware Store or 3€/Meter

Felt furniture glider pads, 40 for €1 in a Dollar Store.

Two pipe end covers 100, better 125mm, or empty soup cans have been working too ;-)

If you care contact me, I have a Sketchup file with the various prototypes for 76/700 and 125/900.

After we finished moving, I'll build the design with a larger base and finish a guide.

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As said above, almost any scope is better then no scope. This scope is not the best,but it certainly is not the worst. It looks from the outside to be in good condition. Hopefully the mirrors are also. It doesn't have the largest aperture but thats neither here nor there REALLY. For what it is, it should give very nice views of the moon and ok views of the inner planets.

Its a keeper for sure. Once you get to know it you may keep it or bin it. I cant see any reason to bin it though.

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Certainly not a rubbish 'scope, and [removed word] should give you amazing views of the Moon, show you the Moons and cloud belts of Jupiter, and Saturn's rings (And on a good day, Titan). It should also give you a nice taste of deep sky, particularly the Orion nebula, and Andromeda galaxy. I should know - I started out with a 70mm (Though it was a refractor)

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I'm glad to hear some of the decent reviews on this scope.

Ok couples questions. Seems like the standard eyepiece size is 1.25" correct? My scope has an 1.25" RK 20mm. So could I get a couple more 1.25"s which I could end up using on another scope if I should upgrade in the future?

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