2X Teleconverter With RF100-400mm vs a Longer Lens

[Cantrell]

All,

I have a R10 and use the RF100-400mm lens. On a recent trip to the Texas Gulf Coast I took pictures of birds flying, but they were too far away. Could not make any details of the birds. Would the 2X teleconverter be an option or do I need to consider a longer lens? Information states that the converter and lens are compatible. Any and all comments are appreciated. 

[ctitanic]

The ideal lens is the one that works the best in your particular situation. I go birding in areas with poor light and lot of vegetation. I owned the RF100-400 and it was too slow for me at f/8. That was the main reason why I traded for the EF. The RF200-800 will put me back in the same situation that did not work for me. 
This is the main reason why I try to avoid giving recommendations about lenses for Birding or Wildlife photography, what works for me may not work for you. 

[Tronhard]

Absolutely Frank, I agree - that is why I prefaced my post with "I think this is a case of situational requirements. "   In case I was not clear, I meant that what each of us favours depends on our situation - which is completely in line with your approach.

Funnily enough, I often shoot in deep bush - so not the different from your expressed situation.  The bird on the left of the two images I posted was in exactly that kind of environment - to get that image you will note both the shutter speed and ISO I used.   There are so many variables in the environment, what settings we use, our camera body and the subjects themselves, but given we are being asked for our perspective on lenses in this situation, all any of us can do is express the pros and cons as we understand them within the context of the information we receive from the writers.   

Forgive me if I am slightly bemused with your comment :"This is the main reason why I try to avoid giving recommendations about lenses for Birding or Wildlife photography,") after it seemed you did express your opinion: "For birding I find 100-400 most of the time adequate. So all depend on the needs.  800mm I think that it's too much for Birding. The maximum I would go would be 600mm"   Perhaps I am misreading your intent.  Either way, that is your experience and I am absolutely fine with that.

It think there is a consensus that teleconverters are one solution but something of a compromise, and the best results will come from getting an optic that is natively designed for the job.  In wildlife that means reach, but how much reach again, is not a constant.  The other constraint, always there is the cost and what one will carry.

[Cantrell]

All,

Thank you again for your responses. If I used the term adapter I meant teleconverter. I have Mount Adapter EF EOS box on my desk.

Reese