<p>I have recently built a 4.5inch reflector telescope. The primary mirror is of 900mm focal length. The issue is, when I try to observe Saturn I am not getting good images. It looks like kind of double images of Saturn. The image gets clear when I cover around half of the telescope opening using my hand. This is the first time I am using a reflector. And i am using a 10mm kellner eyepiece. What could be the possibile issues here? I have collimated the telescope using the collimating cap. But still it gives the same result. What is the chance of secondary mirror causing any diffraction? Or is it due to the primary mirror deffect?I examined the mirror several times but didn't found any deffect.<a href="https://imgur.com/a/Zq632gq" rel="nofollow noreferrer">images of the telescope</a>`</p>

CC BY-SA 4.0
2023-08-20T14:05:34.907Z
If it's when you cover a specific part of the objective/secondary, then it's an issue with the mirror(s).
Greg Miller
CC BY-SA 4.0
2023-08-20T15:03:04.953Z
I checked it...I am getting clear images if I cover from any side of the telescope opening. To check whether it is any damage of my primary mirror I tried rotating primary mirror. But still it is showing same issue .....
sanoj
CC BY-SA 4.0
2023-08-21T23:41:05.193Z
potentially related: [Why does this large Newtonian telescope's front cover have two or three holes in it?](https://astronomy.stackexchange.com/q/38853/7982)
uhoh
<telescope><newtonian-telescope>
Getting good images only when I cover the part of telescope opening
sanoj
# Getting good images only when I cover the part of telescope opening

(Asked by: username_0 on 2023-08-19)

I have recently built a 4.5inch reflector telescope. The primary mirror is of 900mm focal length. The issue is, when I try to observe Saturn I am not getting good images. It looks like kind of double images of Saturn. The image gets clear when I cover around half of the telescope opening using my hand. This is the first time I am using a reflector. And i am using a 10mm kellner eyepiece. What could be the possibile issues here? I have collimated the telescope using the collimating cap. But still it gives the same result. What is the chance of secondary mirror causing any diffraction? Or is it due to the primary mirror deffect?I examined the mirror several times but didn't found any deffect.[images of the telescope](https://imgur.com/a/Zq632gq)`

**Tags:** telescope, newtonian-telescope

> **Comments:**
> **username_1**: If it's when you cover a specific part of the objective/secondary, then it's an issue with the mirror(s).  
> **username_0**: I checked it...I am getting clear images if I cover from any side of the telescope opening. To check whether it is any damage of my primary mirror I tried rotating primary mirror. But still it is showing same issue .....  
> **username_2**: potentially related: [Why does this large Newtonian telescope's front cover have two or three holes in it?](https://astronomy.stackexchange.com/q/38853/7982)  

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## 0 answers

