EOS R100 will not take pictures in M with Vivitar telephoto lens

[nisek]

I am very happy with my EOS R100 and decided to buy a long lens to bring wildlife in closer. Lens is a Vivitar 500mm/1000mm f/8 Manual Telephoto Lens. It came with a lens adaptor. After installing the lens, it will focus perfectly. I put the camera in manual mode. When I engage the shutter, the camera will not snap a picture. Am I missing something in the setup menu?

[shadowsports]

Greetings,

The first thing you'll want to do Is it is enable release shutter without lens attached option.

This is found on the (custom function) C.Fn4 menu.  Visit the link below and scroll down a bit.

https://support.usa.canon.com/kb/s/article/ART183762

The issue might also be related to the adapter you are using, and possibly the lens itself. 

If you'd like to provide more information about them (models, etc.) that may be helpful.

I would recommend sticking with Canon glass and adapters for best performance and compatibility.  Currently, Sigma and Tamron are the only 3rd party lens manufacturers licensed by Canon in the RF Mount.  

[shadowsports]

I see what you purchased now.  Lens and  T mount to RF-S adapter.  I'd like to provide some context and give you some things to think about.

First of all, congratulations on your mirrorless purchase.  The R100 is Canon's entry level and most basic mirrorless body.  However, it tells us that you recognize the importance of an interchangeable lens camera and want performance beyond what a mobile device can provide. 

Lenses are the real investment in photography.  Body's will come and go.  Your lenses if done right will move forward with you.  

Lenses like the one you purchased are somewhere between toy and hobbyist level.  Yes they will take photos.  Will they be of high optical quality, not really.  It depends on what you're looking for. 

It's likely my suggestion above will allow you to take pictures with this lens.  

While the R100 is a entry level camera, it still has a great 24MP sensor capable of capturing some great photos.  I just want you to understand that the quality of lenses you choose can impact its ability to perform.  

You can decide if the images captured  with this lens meet your expectations.

[Ron888]

I think Rick has nailed it.Those lenses have no electronics, so your camera thinks there's nothing there.
I'm curious - do you have the conventional lens (over a foot long) or a mirror lens (super short,about 6 inches)?