I'm able to focus only while using 25mm with an extension tube

[takaeri]

Hello everyone, Im new to all of this and just got my own telescope, its 130/920 eq2. Im able to clearly see the moon and jupiter (barely) but only when I use 25mm with an extension tube, same goes for terrestrial objects such as distant chimneys or mountain tops. Besides 25mm and an extension tube I also have 10mm, 1.5x erecting lens and 2x barlow lens but no matter what i use and combinate, the image is out of focus and blurry (im seeing black circle with like 4 strings I read somewhere that Im seeing secondary mirror). Any ideas what should I do? 

[Mandy D]

@takaeri Yes, you often need extension tubes to bring a Newt to focus. If you cannot get focus on the Moon with the focuser fully racked out, try sliding the eypiece backwards out of the focuser. You may need more extension than you have available. You can buy them readily. Get focus on a distant object in daytime first as it is far easier than fiddling in the dark. Then, at night, aim for the Moon as it is bright and easy to work with. Good focus on the Moon will be fine for everything else in the night sky. Start with the 25 mm eyepiece, no barlow. The 10 mm is probably not going to be very good and I would forget the barlow that comes with these telescopes, altogether.

[Bugdozer]

22 minutes ago, Mandy D said:

@takaeri Yes, you often need extension tubes to bring a Newt to focus. If you cannot get focus on the Moon with the focuser fully racked out, try sliding the eypiece backwards out of the focuser. You may need more extension than you have available. You can buy them readily. Get focus on a distant object in daytime first as it is far easier than fiddling in the dark. Then, at night, aim for the Moon as it is bright and easy to work with. Good focus on the Moon will be fine for everything else in the night sky. Start with the 25 mm eyepiece, no barlow. The 10 mm is probably not going to be very good and I would forget the barlow that comes with these telescopes, altogether.

Question: why do manufacturers make telescopes that are intrinsically impossible to focus without an additional device? That seems crazy. 

[Mandy D]

14 minutes ago, Bugdozer said:

Question: why do manufacturers make telescopes that are intrinsically impossible to focus without an additional device? That seems crazy. 

No, it's not crazy. You cannot gain extra inward focus without re-engineering your telescope. It is for things like imaging with DSLRs and for accessories to be fitted for imaging that require more back-focus.

 

[Bugdozer]

22 hours ago, Mandy D said:

No, it's not crazy. You cannot gain extra inward focus without re-engineering your telescope. It is for things like imaging with DSLRs and for accessories to be fitted for imaging that require more back-focus.

 

I don't understand your explanation. The OP is trying to use it visually as far as I can tell. By default, the telescope should be engineered to work properly for visual observation. I understand the need for extension tubes etc with things that require a specific distance for the focal plane such as photography, but this doesn't appear to be that situation. Or am I missing something? If a scope requires extension tubes in order to be used for visual observation, then they should come as part of the scope when you buy it, not have to be purchased separately. 

[Jim L]

On 20/01/2024 at 14:04, takaeri said:

Hello everyone, Im new to all of this and just got my own telescope, its 130/920 eq2. Im able to clearly see the moon and jupiter (barely) but only when I use 25mm with an extension tube, same goes for terrestrial objects such as distant chimneys or mountain tops. Besides 25mm and an extension tube I also have 10mm, 1.5x erecting lens and 2x barlow lens but no matter what i use and combinate, the image is out of focus and blurry (im seeing black circle with like 4 strings I read somewhere that Im seeing secondary mirror). Any ideas what should I do? 

If Mandy’s suggestion works take note of how much you slid the eyepiece out of the visual back and source an extension tube that results in most of your eyepieces coming to focus when your focuser is racked out about midway. It’s annoying to have to get additional unplanned gear, and getting the right length extension tube will take some measuring and a bit of math, but that will likely solve your problem permanently.

 

Edited January 21 by Jim L

[happy-kat]

Welcome. I'd take a step back and put your 25mm in the focuser, remove the telescope end cap, aim the telescope at a distant target like the Moon, slowly wind the focuser all the way in, and then out to find focus and enjoy the Moon. Next swap the eyepiece for the 10mm, repeat with slowly winding the focuser in then out finding the focus spot. For general observing with your telescope and an eyepiece I wouldn't expect an extension tube to be needed 

[Mandy D]

12 hours ago, Bugdozer said:

I don't understand your explanation. The OP is trying to use it visually as far as I can tell. By default, the telescope should be engineered to work properly for visual observation. I understand the need for extension tubes etc with things that require a specific distance for the focal plane such as photography, but this doesn't appear to be that situation. Or am I missing something? If a scope requires extension tubes in order to be used for visual observation, then they should come as part of the scope when you buy it, not have to be purchased separately. 

OK, the point is that to achieve sufficient inward focus for my Nikon DSLR to achieve focus requires me to wind the focuser in an additional 46.5 mm just to make up for the fact that the sensor is buried so deep into the camera's body. We could, theoretically, achieve this by using a focuser with a lot more travel than you generally see fitted to Newtonians, but, then the focuser would intrude into the tube further and block precious light.

I have absolutely no argument with you about the fact that extension tubes should be supplied where necessary to focus with any supplied eyepieces. But, the end user has the option to buy other accessories (eyepieces included) that require more extension (or none!). Why should the telescope manufacturer supply everything that everyone will ever want to use with the telescope?

Try purchasing an imaging scope, like my RC6. You will rapidly find that accessories are absolutely required beyond those included with the OTA. Hell, it didn't even have a single eyepiece or finderscope included! I bought an additional pair of 50 mm spacers for mine.

I'm guessing that the OP has bought this kit used and does not have all the original accessories. In any case, it is a simple matter to acquire the necessary parts, as I have explained in my reply to him.

I hope this helps.

[Bugdozer]

7 hours ago, Mandy D said:

OK, the point is that to achieve sufficient inward focus for my Nikon DSLR to achieve focus requires me to wind the focuser in an additional 46.5 mm just to make up for the fact that the sensor is buried so deep into the camera's body. We could, theoretically, achieve this by using a focuser with a lot more travel than you generally see fitted to Newtonians, but, then the focuser would intrude into the tube further and block precious light.

I have absolutely no argument with you about the fact that extension tubes should be supplied where necessary to focus with any supplied eyepieces. But, the end user has the option to buy other accessories (eyepieces included) that require more extension (or none!). Why should the telescope manufacturer supply everything that everyone will ever want to use with the telescope?

Try purchasing an imaging scope, like my RC6. You will rapidly find that accessories are absolutely required beyond those included with the OTA. Hell, it didn't even have a single eyepiece or finderscope included! I bought an additional pair of 50 mm spacers for mine.

I'm guessing that the OP has bought this kit used and does not have all the original accessories. In any case, it is a simple matter to acquire the necessary parts, as I have explained in my reply to him.

I hope this helps.

That explains it a little more clearly. If components are missing from the kit, then obviously third party extras may need to be purchased. However, I stand by my view that if a retailer is selling A Telescope Set as new (i.e. not just components individually such as the OTA or tripod) then it should be usable in its sold state for visual observation, in other words it should contain some sort of mount, an eyepiece, and a means of enabling that eyepiece to be brought to focus. Just like my SCT came with a diagonal, because without it, it's physically impossible to look at anything above a certain altitude. 

The analogy with buying an imaging scope OTA doesn't really apply because the OP appears to have purchased a complete kit rather than assembling one from components. It's reasonable to assume such a kit would be usable as sold. Otherwise you have a case of misleading advertising, unless the seller was explicit that extra items would be required for even the most basic use.